Just look at him now. Top of the world.
Here's a revealing statistic. McCullum's test batting average is 38.09. His average as skipper after 14 matches is 50.95. That tells a tale.
He got rid of the run bogey with a welcome century in the first test against the West Indies in Dunedin early in December and has soared to new heights as he has inspired New Zealand to beat mighty India, first 4-0 in their ODI series, and now 1-0 in the two-test rubber which ended yesterday.
And he's led from the front. It's a hoary old line but captains who lead by example are generally the most secure in their job.
On that score, since returning from an embarrassing limited-overs beating in Bangladesh in October, McCullum has been in superb form.
His 302 scaled a New Zealand cricket Everest. Sit it alongside Sir Richard Hadlee's nine for 52, and 15 for 123 to beat Australia in Brisbane in 1985, or ahead of it? Take your pick.
It was one mountain New Zealand had yet to climb. Before yesterday, New Zealand was the only major test-playing nation without a triple hundred maker.
What made McCullum's innings at the Basin Reserve extra special were the circumstances, having to pull New Zealand up from a hopeless position midway through the third day.
History was a handful of good blows away when he walked on to the ground yesterday morning. By nice symmetry it was where Martin Crowe hit his epic 299 23 years ago and which McCullum aimed to eclipse.
It took him 32 balls to get from his overnight 281 to 300, achieved with a cut to the third man fence.
The standing ovation was loud, heartfelt and long. The crowd had clapped defensive shots along the way, urging the skipper onwards.
When he completed the job it seemed they didn't want to resume their seats.
A double century followed by a triple; only Australian legend Don Bradman and Englishman Walter Hammond - against New Zealand in 1933 - have managed that. McCullum is in rare company.
The mind goes back to his test debut. He was the wicketkeeper, young, lively and clearly with talent to burn. There was a half century against South Africa in Hamilton in 2004 in that match, and at a brisk rate. McCullum was a man in a hurry from the start.
There have been centuries along the way, including a double century in Hyderabad in 2010 when he started opening the batting.
He likes India. He's taken two double hundreds and the triple off their bowlers.
This is a special moment in New Zealand sport, let alone cricket.
Crowe was magnanimous towards McCullum. Records are, after all, meant to be broken.
And it was fitting that the captain, who has done so much to lift New Zealand after a grim first 10 months under his stewardship, should reach the milestone first.
It was also a fitting way to end a summer of considerable personal and team achievement.
McCullum the magnificent
Brendon McCullum's 302 is the highest individual score by a New Zealander in a test.
He batted for 775 minutes - the eighth-longest innings in tests - faced 559 balls, hit 32 fours and four sixes
It was McCullum's ninth test 100 and third in the space of five tests.
Only Martin Crowe (17), John Wright (12), Nathan Astle and Ross Taylor (11) have scored more test hundreds for New Zealand.
McCullum joins Australians Don Bradman and Michael Clarke as the only triple centurymakers batting at No5.
McCullum, Bradman and Walter Hammond (England) are the only players to have scored a double and triple century in consecutive tests. Bradman also did it the other way around.
McCullum scored 535 runs in the two tests against India, trailing Sri Lanka's Sanath Jayasuriya (571 against India in 1997) and Hammond (563 against New Zealand in 1933). All three scored a triple 100 in those series.
