Despite his all-round skills, the England international's first job will be to ramp up a leaky defence.
Gary Cahill to have Chelsea's back
There is, of course, another interpretation, one that Chelsea prefer. An England international centre-back, one who has combined profitably with John Terry in the past, was available for a cut-price fee of £7 million (Dh39.9m). So as he prepares to debut at Norwich on Saturday, which is the real Gary Cahill? A player who can be blamed for Bolton's traumatic season or a defender rated not just by Villas-Boas, but by Fabio Capello and previous suitors Arsene Wenger and Harry Redknapp?
The answer, perhaps, is both. Despite the myriad of mistakes made by Dedryck Boyata, David Wheater, Zat Knight and Paul Robinson at the back for Bolton this season, Cahill has been culpable. His reputation rests more on past performances than present.
It is worth remembering that Martin O'Neill, whose central defenders tend to be stoppers, sold Cahill when at Aston Villa. Unlike the Northern Irishman's preferred partnership at the time, Martin Laursen and Olof Mellberg, Cahill plays with more ambition.
It can be his undoing. He was dismissed at Tottenham for a foul on Scott Parker that followed a Cruyff turn in his own half. The decision was overturned on appeal, but Cahill misjudged the situation.
Yet the contributions that bookended his Wanderers campaign illustrate his appeal. In August, he struck from 20 yards with an arcing shot against QPR. On his Bolton finale, Cahill finished like a striker to secure victory at Everton. He is a rare central defender, one capable, in his Villa days, of scoring an overhead kick in a derby.
His finishing was a factor Terry mentioned in outlining his potential partner's qualities. "He reads the game well, he's got a bit of pace and he's good in the air," said the England captain. "And he scores important goals."
His manager's words emphasised the attributes he values highly. "He had good technical abilities, which is important in the way we want to play and to implement our passing philosophy," Villas-Boas said.
The task is to be footballer first, defender second. Speed of distribution and speed of foot are equally important.
In Chelsea's much-discussed high defensive line, a centre-back with the pace to recover is essential. If his full-backs are directed to overlap as enthusiastically and as often as they have done, it matters even more that there is mobility in the middle. The slower Alex has been deemed surplus to requirements while the quick, but erratic, David Luiz remains in the team.
Speedy, all-round footballers who are willing to take a risk, there are similarities between David Luiz and Cahill, but the view at Bolton is that the latter offers more dependability. "Gary has tremendous mental character," said Owen Coyle, his manager at Bolton. "He is a fantastic player and a genuine lad."
The Scot rarely criticises his players so praise was to be expected. However, it was notable that Coyle continued to name Cahill captain even after Bolton had accepted Chelsea's offer; Cahill was in limbo when he secured the Goodison Park triumph.
Yet goalscoring is not his prime responsibility. As Chelsea's new No 24 begins life at Stamford Bridge, it is in a defence that has kept a mere five clean sheets, two fewer than relegation-threatened Fulham, and only three more than Bolton.
Villas-Boas may now have England's first-choice centre-back duo but Cahill's task is to prove he is the plug to shore up a leaky rearguard, and not just David Luiz with more sensible hair.