They can be the trusted representative of a player or the bane of club management, but there's no dispute that agents and advisors play a major role in English football.
Football agents: A valued ally or a 'necessary evil'?
One aspect of his high-profile position working for the Premier League club he probably will not miss, however, is having to indulge Kia Joorabchian.
Joorabchian, an Anglo-Iranian businessman, claimed he helped Cook land the job at City and "increased his salary more than four times" from what he was earning at his previous job, with Nike.
Their relationship, however, deteriorated dramatically: Joorabchian became Cook's bete noir.
The distasteful email which led to Cook's resignation concerned the mother of the City defender Nedum Onuoha. Joorabchian had told BBC Sport there was "a level of interest" in clubs looking to sign Onuhoa.
Yet last week, just days after the 11-month-old email surfaced, Joorabchian denied he advised or represented the player. It is no wonder that senior figures at City believe Joorabchian was involved in the leak of the email that precipitated Cook's demise.
Joorabchian is an unlicensed football agent, yet whatever you call the men who work on behalf of players - agents, advisers, representatives - the Onuoha episode highlights the power they can wield.
With Premier League clubs paying £67m to agents in the 12 months up to November last year, the stakes are high and business is brisk in the billion-pound industry of signing players.
In 2007, the forthright Gary Neville, the now-retired Manchester United defender, called for "the removal of agents from the game", arguing that players did not "need people taking hundreds of thousands of pounds off them, just good advice from a solicitor or an accountant".
Greg Keenan, the chief executive of Aspire Management, is puzzled by the negative publicity surrounding agents. "When you operate in a sport where there is a lot of money at stake then there is bound to be criticism. It goes with the territory," said Keenan, who counts Lars Lagerback, the former Sweden coach, and Kanu, the Nigeria striker, as clients.
"It really doesn't bother me, and one thing you learn over the years is that there is no point losing sleep over something that you cannot control. At the end of the day, what matters is that clients are happy."
Terry Robinson, who spent two years as chairman of Sheffield United, describes agents as "a necessary evil".
"If players don't want them, then they have no role to play," he said. "But the players do want them as they don't always have the confidence to negotiate their own deals."
Football agents, it seems, are no different than operators in any industry: some are upstanding; some are rogues.
"You get bad estate agents," said Clive Hart, who works with 20 players as a consultant for Select Sports Management. "Everyone has a horror story from an estate agent but newspapers aren't interested in a bad story from an estate agent as football is more in the public eye."
Brian McDermott, the manager at Reading, concurs. "You get good and bad agents just like you get good and bad managers," he said.
Richard Lee, the former England Under 21 and Blackburn Rovers goalkeeper who is now plying his trade in the third tier of English football for Brentford, certainly had a bad one.
"After playing for England U21s I had a dozen agents ringing me," Lee said. "I eventually signed with one but as soon as he signed me, I never heard from him for two years. I even had to negotiate my own deal when my contract was up at Watford. I then got a letter from him saying I owed him £7,000 commission. Legally, I had to pay it."
Agents are usually paid a percentage of a player's total contract, normally between five and 10 per cent.
Tor-Kristian Karlsen, the consultant who advises a number of clubs about players in South America, Eastern Europe and Scandinavia, told BBC Sport in an interview last year the fees agents charge clients are not commensurate with the work they put in.
"If you hire a lawyer to do the same job, he'd more than likely charge a standard hourly rate which isn't directly linked to the player's end salary," Karlsen said.
A Scotland international interviewed by The National said he felt his former agent did not warrant the £350,000 he claimed he was owed for his part in the player's lucrative move to the Premier League. The matter went to court.
"When you're trying to concentrate on the football the last thing you need is some guy who's not done a great deal for you pestering the life out of you and having to go to court," said the player, who asked that his name not be used.
"I was having to miss games. I was trying to fight for my place, the manager wanted me there in the squad, and I'm having to tell them 'Just to let you know, I'm not going to be here today because some agent is suing me and I need to be in court'."
Agents themselves are not immune from being betrayed, according to Hart.
"I worked with a client for seven years," said Hart, who represents, among others, Shane Ferguson, a promising left-sided player at Newcastle United.
"The relationship was getting stronger and stronger and then he rang me up one day and said he was going somewhere else. From a business point of view it's disappointing but it's also disappointing personally, too.
"But that's football. Any agent who tells you he's never lost a client is a liar."
Tommy Smith, the Queens Park Rangers forward, is represented by Steve Kutner, who also looks after Frank Lampard. Kutner prefers to keep his client list small so he does not spread himself too thin. "Steve is great and I can't speak highly enough of him," Smith said. "I must have had meetings with 20 agents over the years but it's important you use your intuition, speak to senior players in the team, work out who you can trust and then who would I want going into a room to represent me."
Kutner has overseen Smith's moves to Watford, Portsmouth and QPR. Smith acknowledges agents are a club's "worst enemies but they are a necessity for players".
That concurs with a point made by Robinson, who is now the director of Stoke City's academy and, presumably, is relieved he no longer has to pull up a chair at the negotiating table and haggle with a player's representative.
"I had one bad experience," Robinson said. "We agreed a deal in principle with a player. Him and his agent went outside to have a chat and we never saw them again. They went and signed for another club.
"There was no word or anything."
McDermott recalled a similar episode when he tried to sign John Mensah, the Ghana defender, in 2006. "We thought we had him and we had his agent but it turns out his agent was someone else and we lost him," McDermott said.
Agents encounter difficulties of their own. Hart, for example, was negotiating a move of a player to a club in the second tier of English football in the summer when a problem arose.
"The fee was agreed, the contract was agreed and the player was happy," Hart said. "But the player's dad was in the room at the signing and he started questioning the amount of free accommodation his son was getting. I had to call up the chairman the next day and apologise. He took it in good spirit and the deal went through, but that's not cricket."
Steve Bruce, the Sunderland manager, described the people surrounding Asamoah Gyan, his striker, as "parasites" after the Ghana striker secured a surprising move to Al Ain last week. Bruce claimed that Gyan's complex management team "unsettled" the player during Ghana's friendly with England at Wembley in March.
McDermott recalls the days as a young professional at Arsenal in the late 1970s and early 1980s when his first agent would station himself outside the car park at Highbury "and offer insurance policies to players".
Bernard Halford is life president at Manchester City. He is in his 51st season in football administration, having served as City's club secretary for 39 years after a decade at Oldham Athletic. He said the rise in prominence of the agent is the biggest change in football.
"In previous years you would get players with a club sometimes all their life. Now agents are unsettling players and trying to move them. You don't even see the player during negotiations. If you don't agree with the agent then you don't get the player."
McDermott validates Halford's claim. He joined Reading as chief scout at the turn of the millennium before progressing to become the manager in 2009.
"I've really noticed the influence of agents from 2000 onwards," he said. "When Reading got into Premier League in 2006 if you didn't know the right agent then you didn't get the right player. It was as simple as that."
Tony Pulis, the Stoke City manager, endured a similar experience when his unfashionable team were promoted in 2008.
"There weren't a lot of agents who wanted to deal with us as they couldn't see us doing anything except getting relegated," Pulis told BBC Radio 5 Live. "Agents who were not big names helped us out immensely.
"If I ever do business I always try to push the business their way because they helped me right at the beginning. There were other agents who used this football club to get better deals elsewhere. It's changed now as we are more established and they are more subservient as they want to do business with us now."
With the likes of David Trezeguet and Maicon on his books, Antonio Caliendo is a leading agent.
He does business, by and large, with the bigger clubs. He contests the suggestion that agents "want their players to change clubs to earn more money".
"It's not true," Caliendo said. "There are bad people in the agents' categories, as there are in club directors and footballers. So, agents are not always right but not always wrong."
Caliendo said that he not only acts on behalf of the player when negotiating wages, but also provides financial advice and help with endorsements, sponsorship and media relations.
A qualified lawyer, Keenan has worked as a sports agent for 16 years. He looks after the affairs of around 20 of Aspire's 100 clients across both football and rugby.
"Sometimes we simply broker a deal acting as an agent, and sometimes we manage the client so that we are involved in all their business affairs, including sourcing commercial opportunities, controlling PR, arranging tax advice and overseeing investments but do not 'manage' the coach or player."
The bulk of agents' work, though, concerns transfers and they can play an instrumental role in pushing through deals.
"With some clients it can be a contract negotiation role, others a promotion role," Hart said. "For example, if David Beckham is your client you don't need to approach a chief scout and say 'What do you think? He's got a good right foot, hasn't he? But with lower-league players and foreign players you need to promote them.
"But, going back to Beckham, if you have 10 Premier League clubs interested in him then I would help with the contract negotiations."
Hart has been working in football since 1998 and been a licensed agent since 2002, yet 70 per cent of international transfers are concluded using unlicensed agents. English clubs are prohibited by the English Football Association, in the strongest terms, from involvement with unlicensed agents at any stage of a proposed transfer.
Many agents believe that Joorabchian provides services which fall under the FA's definition of "agency activity" and so should be subject to the same rules and scrutiny as they are. Joorchabian insists that he is not an agent.
Licensed or unlicensed, Lee, the goalkeeper, issued a stark warning to emerging players who are inundated with requests from prospective agents.
"Agents all promise the same thing and there are a lot of sharks out there and it's a dangerous business," he said.
Smith played with Lee at Watford and offers similar words of advice for his fellow professionals, particularly the young players.
"You definitely need an agent," said Smith, 31. "It can take a couple of years to get the right one. They do a lot of work players can't do and sometimes they find it easier to talk to the manager than the player and vice versa. If you haven't got an agent it's not the easiest thing to do to ring clubs and say you are available."
Keenan believes every player "needs a good agent in their corner".
"An agent's role is to add value," he said. "It's hugely important and it comes down to a footballer aligning themselves with someone who is professional and who they trust.
"Generally, if you act professionally and if you've got something the club wants, then you won't have a problem. The name of the game is being flexible and being able to quickly adapt."
Managers have agents, too. McDermott has a representative and they speak most days. He believes "the best ones are the ones you talk to regularly. We have a good relationship".
Hart likes to have a rapport with his clients. "It's a personal business," he said. "You are not moving furniture."
McDermott is thankful that he does not have to sit on the sofa in the office of John Madejski, the Reading chairman, and listen to the demands of players' agents.
Nicky Hammond is the conduit between chairman and manager. News of the deals are relayed to McDermott.
"From my point of view it shouldn't be about money," he said. "It should be about the career of the player and the best environment. Sometimes it will not be in an agent's interest to take a player to your club as they will get more for taking him somewhere else.
"Agents in Premier League are different breed, like Pini Zahavi and Kia Joorabchian. But in lower leagues you get agents ringing you up you don't even know. You would get calls saying 'What are you looking for?' Any good agent has to do their homework. If I'm interested in a centre-half and they offer me one then I'll listen."
Hart clearly has the ear of many managers and scouts the length and breadth of the United Kingdom.
"Any agent tells you he is equally well connected at all 92 clubs and 12 [Scottish Premier League] clubs then he's pulling your chain," Hart said. "You make friends, as you do in life, at certain clubs but those contacts move around. So you can be the most well-connected agent at a few clubs but then when those contacts move around you lose that connection.
"With a player coming out of contract is where you have to be most proactive. Because when their contract runs out, they haven't got a job."
TOP FIVE DEAL MAKERS
Brokered his first deal in 1979 by taking Avi Cohen to Liverpool and has not looked back. Has handled two moves by Rio Ferdinand worth over £48 million (Dh278.5m) and, for a period, brokered every major deal at Manchester United. Was central to Roman Abramovich's acquisition of Chelsea in 2003.
The Portuguese former bar owner netted nearly £4m after negotiating Cristiano Ronaldo's move from Manchester United to Real Madrid in 2009. With clients such as Jose Mourinho, Nani and Falcao it is no wonder he is arguably the richest and most powerful agent in world football.
The Brazilian has used his connections in his home land to make millions, particularly from moving Robinho to Real Madrid, Manchester City and AC Milan. Neymar, the highly-rated Brazilian, should ensure he is kept busy and well remunerated over the next few years.
Born in Italy but naturalised as a Dutch citizen, Raiola has made his fortune from negotiating deals for some of the cream of attacking talent in Europe, such as Dennis Bergkamp, Zlatan Ibrahimovic and Mario Balotelli. Railoa was previously a pizza restaurateur.
His father's former position as the Arsenal vice chairman helped him add Thierry Henry, Cesc Fabregas, Gael Clichy and Robin van Persie to his growing list of clients.