In his sixth-form year he was selected ahead of Dan Carter as first five-eighths for the South Island's secondary schools side. On another occasion, he played for the school's first XI football side at 1pm in an inter-school against arch-rivals Otago Boys' High School and then led the first XV at 3pm to their first win away from home in 24 years. McCullum, of course, scored a brilliant solo try.
Last week he was named the 28th captain of the New Zealand cricket side. It didn't come about in the way he might have hoped, as coach Mike Hesson ousted Ross Taylor, and McCullum considered all options when asked to take over in all three formats. He decided to accept "for the good of the team".
Those who know him well say he will do a good job and will be "aggressive" and "instinctive". Others are less convinced, believing his personality is not suited to being New Zealand captain.
"He's up and down like a yo-yo," said one well-placed source, who spoke on condition of anonymity. "He's all over the place. It's about sound decision making and we have seen at the crease you don't get that too often with Brendon. Personally, I don't think he's captaincy material."
There are few more divisive figures in New Zealand cricket. He's often perceived as brash, perhaps even cocky.
McCullum has Roman numerals stencilled on his right shoulder and bicep that refer, among other things, to his playing number (42) and the birthdates of his children. It's a public display of the importance of family and one of the strong themes that emerge when talking to people who know him well.
He comes from one of the most prominent sporting families in Dunedin. His father, Stu, played first-class cricket for Otago, uncle Grant was a wicketkeeper who found his way to the Otago side blocked by Warren Lees and his brother Nathan is a teammate at both domestic and national level.
The young McCullum was a dressing-room rat - a kid who spent time in the dressing room at Culling Park as his father played club cricket for Albion. Brendon and Nathan were omnipresent and even played as substitute fielders for Albion's premier team when 8 and 9 respectively when a number of players were sitting university exams. Their arms, according to former Albion president Warwick Larkins, were better even then than those of most senior members of the side.
His son, Riley, is said to have also taken on those traits as he immerses himself in his father's world. "He's great with kids," says former Otago and New Zealand teammate Craig Cumming. "My kids have had a little to do with Brendon and they don't look at Brendon as McCullum the superstar or cricketer. They actually look at him as a friend who plays cricket for New Zealand and they do that because of the way he treats them. It's a nice trait, a special trait. These are the things people don't see and don't understand. Off the park he is a very generous, courteous and honest bloke."
It's a view shared by his King's High School 1st XI coach John Cushen, who played for Otago in the 1980s. McCullum has often made time to talk to Cushen, even after a test win, when teams traditionally celebrate among themselves. "That's not an arrogant, stuck up, hip-hopper," Cushen says. "I have just found him to be respectful and respectful of the people I'm around. He's not cocky or arrogant."
McCullum even followed Cushen's orders when, as a fourth former, he was instructed not to chase 18 runs off the last over in an inter-school against Southland Boys' High, when King's were nine down.
"In those days you never lost and I sent out instructions that we were not going for the win," Cushen says. "He said, 'I can do this.' I told him again, 'We're not going for this.' He didn't go for it ... but he probably wasn't overly happy about it."
King's played an important role in McCullum's life - although his teachers say he went to play sport rather than learn - and still does. The McCullum brothers set up a cricket academy at the school and in 2002 Brendon returned to his alma mater to present the school with his first New Zealand shirt.
It was something he felt inspired to do after seeing, as a student, Carl Hayman do the same thing when he made the All Blacks.
"I was there when Carl donated his jersey to the school and it gave me a real buzz," he told the Otago Daily Times. "It's great to be able to do the same thing now that I've played for my country."
McCullum's first taste of international cricket was far from appetising. After devouring provincial and age-group bowlers - he played at a junior world cup and made his first-class debut for Otago while still at high school - he struggled at the highest level and confronted criticism for the first time in his career.
He posted single-figure scores in 14 of his first 20 one-day international innings and it gave critics who questioned his selection at such a young age, of which there were many, plenty of fodder. The selectors perservered and McCullum never doubted he would succeed.
"He was very much full of confidence but, when he was younger, it was probably too much confidence," Cumming says. "Over time he's certainly grown up.
"I just love his confidence. The world was there to be taken and that was the way he saw it. He saw every day as an opportunity to do something special. It was an outlook a few of us playing the game probably wished we had, too. It wasn't always successful and has brought about his downfall, and still does every now and then.
"Cricket is an awful game because you fail so regularly compared to your successes. Even the greats do it. To have that attitude is fantastic."
Notably, he didn't drop his bundle when he missed out last year on the captaincy to Taylor in another messy public process.
He wasn't happy but he didn't undermine Taylor and stepped up to lead the side last summer when Taylor was absent against both Zimbabwe and South Africa.
Away from the cricket pitch, McCullum enjoys horse racing and a quiet beer with friends. He hasn't led a totally clean lifestyle in an era when players are often expected to be pillars of purity, but he doesn't live to excess.
It's said McCullum would always smoke a team fitness test regardless of what the previous evening entailed, which caused some alarm among team management. McCullum is a naturally gifted athlete and cricket staff worried that younger and more impressionable teammates might think they, too, could follow his example.
Former New Zealand batsman Craig McMillan is now close friends with McCullum and the pair's children play cricket together in Christchurch. McMillan said they've had some fairly "heated discussions" about the state of New Zealand cricket and the team and it's an abrasive relationship that stretches back to the first time they met.
It was when McCullum was about 19 and starting to make waves. Both McCullum and McMillan shared the same sponsor and McCullum broke a bat. The sponsor wanted McMillan, who was playing a first-class game at the Lincoln Oval, to give McCullum one of his.
"He came in to look at my bat and proceeded to tell me all that was good and bad about it," McMillan says. "Straight away there was that brash 19-year-old. It made me laugh. It made me think, 'Who is this kid?'
"I remember the first net session we had when he made the New Zealand team.
"A few of us thought we would try to test him out. We had heard a bit about him so proceeded to bowl short and give him a real workout. He took everything on. Everything we could dish out, he took on the chin. Straight away I thought, 'There's something about this kid and he's going to be a pretty good player'."
As a player, he probably hasn't yet achieved as much as his talent suggested, but there is a sense of hope he will also become a pretty good captain.
McCullum's greatest hits
Known as an explosive batsman at the top of the order, Brendon McCullum's reputation and fortune were secured when he blazed an unbeaten 158 in the first game of the Indian Premier League for Kolkata Knight Riders. Perhaps surprisingly, some of his best innings for New Zealand have been his most restrained.
Here are the new skipper's five greatest hits for NZ.
1) 96 v England, Lord's, 2004 (test)
In just his fourth test, McCullum was promoted to No 3 in the second innings when Nathan Astle was struggling with flu. In partnership with Mark Richardson, whose dutiful double of 93 and 101 helped fill the bars around the ground, McCullum's spiky innings should have propelled New Zealand to victory and him on to the honours board. Instead he fell to Simon Jones' reverse swing and New Zealand then proceeded to collapse. England eventually cantered to a seven-wicket victory, but McCullum was announced as a serious talent. Four years later he fell just agonisingly short at Headquarters again, this time scoring 97.
2) 86* v Australia, Seddon Park, 2007 (ODI)
People often think of McCullum as a limited overs specialist but the truth of the matter was that when McCullum walked out for his 83rd ODI innings, his one-day record was looking deathly pale. He had reached 50 just four times playing in a variety of positions and his average was a poorly 21.7.
Not that you could tell here.
Coming in at 5-116 chasing an improbable 347 for victory, McCullum first played foil to Craig McMillan (117 off 96 balls) in a 165-run partnership, then showed hitherto unseen maturity in nursing the tail home to victory, his unbeaten 86 coming off 91 deliveries.
3) 116* v Australia, AMI Stadium, 2010 (T20)
Down on one knee, scooping Shaun Tait, he of the 155km/h slingshot delivery, over his and the keeper's head for six. That's probably about all you need to know about this display of sustained brilliance.
A slog sweep off left-arm quick Dirk Nannes was another for the memory banks. In fact, it was pretty much shot-a-ball stuff until he pushed one to deep cover for a single to bring up 100, the crowd going nuts in the background.
You didn't have to like the format to appreciate the skill.
4) 104 v Australia, Basin Reserve, 2010 (test)
This was the most productive year of McCullum's career. He proved he could tough it out at the Basin Reserve, combining with Daniel Vettori on the fourth day to defy a rampant Australian attack and gale-force winds. He ended a hellishly difficult day 94 not out (though was lucky to survive one lbw referral, when the high winds rendered the ball-tracking camera unreliable) and nudged his way to a century early the next day before nicking out.
5) 225 v India, Hyderabad, 2010 (test)
The daddy of all McCullum knocks and part of the reason why what he has done since has been so underwhelming.
McCullum batted like a true test opener in dusty Hyderabad, mixing admirable restraint with his 22 fours and four sixes.
The problem being that his double century was 31 innings ago and he hasn't passed three figures since. It's not as if he's been in a trough, but the 31 he has averaged since his big one does little justice to his talent.
