His appointment, combined with Ben Stokes' ascent to the captaincy, has added a Rasputin-like mystical charm to England's revival with no curfews, no excuses and no limits.
Baz-ball has begun.
Talk of him lacking coaching experience at test level has been silenced as disciples gather and cynics disperse. His man-management capabilities, focusing on the psychological more than the technical, are getting championed with gusto. Anyone who has played 101 consecutive tests and led in 31 of them is bound to have a knack for persuasion and cajoling.
That's where one of McCullum's handiest traits comes to the fore. The ability to "walk with kings – nor lose the common touch" as Rudyard Kipling wrote in his poem If.
He is as comfortable being "Mr McCullum" in the corridors of the Lord's pavilion as he is being "Baz" shouting his round at the Albion club in Dunedin.
Either way, the self-belief McCullum formed as a boy among men during those formative Otago years remains steadfast. He attached like a barnacle to the balcony in both tests, rode the narrative in his new powder blue and overcast grey uniform and sported a poker face - behind his beard and sunglasses - that could win a fortune in Las Vegas.
McCullum is letting his players do the talking now, but on his last tour to England in 2015 he fronted the show as skipper.
His comments have paid a dividend in hindsight.
When the Black Caps went down 1-0 in the two-test series before levelling at Headingley his message was consistent with the one he is promoting now.
At the time the Herald noted McCullum was surprised by a reaction after the Lord's loss which called for them to scale back their aggressive approach.
"Playing this style gives us our greatest opportunity to win the test and the series.
"We went down but played some pretty good cricket throughout, it was a credit to England being good enough to run us down. The more we do that, the more we become comfortable with that, although at times we will be beaten.
"When you lose a test, people's thoughts head in a different direction. The first thing they attack is the way we played our cricket, but I make no apologies."
Ditto 2022... albeit with the plaudits now heaped in his side's favour.
The then-captain also channelled his best Nostradamus.
"For so long we've sat in the doldrums and our performances didn't warrant teams playing us in three-test series. We need to get back to a level of respect where teams want to do that."
This is the first time three fixtures have been scheduled for New Zealand in England since 2008 after two-match teases in 2013, 2015 and 2021.
Even seven years ago McCullum had earned respect. That was reinforced by an invitation to deliver the annual Cowdrey spirit of cricket lecture at Lord's the following year.
Yet he is still communicating.
Part of that is through words, like holding court in team huddles or one-on-one at practice.
The rest is through gum-chewing stoicism that acts as a warning to disrespect his crew at your peril.
McCullum has officially passed his induction as the catalyst to take established talent to new glories.
Next year's Ashes already shapes as a box office bonanza.
