The astonishing innings put him in the company of Shane Warne, Glenn McGrath, Dennis Lillee, Steve Waugh and the greatest of them all, Sir Don Bradman, as a verified England tormentor who now forever owns a significant slice of Ashes history.
Warne took 708 Test wickets, but will always be remembered for his first on English soil.
Like Waugh's last-ball ton at the SCG, the Don's 334 at Headingley or McGrath simply taking delight in humiliating his opponents with predictions of 5-0 cleansweeps.
All embraced and revelled in the Ashes cauldron.
Agar, the aspiring lawyer, took his own approach - measured in everything from his attitude to his backswing.
But with each flash of his blade the records tumbled.
Highest score by an Australian No.11 on debut. Highest score by an Australian No.11 all time.
Highest Australian 10th wicket partnership. Highest all-time 10th wicket partnership.
Highest all-time Test score by a No.11 batsman, overtaking West Indian Tino Best's 95.
And finally, most unbelievable Test innings of all time.
Well, that's not an official record - but how else do you describe a 19-year-old debutant No.11 attacking bowlers with disdain on his way to a near run-a-ball 98?
One who was almost entirely anonymous 30 hours before he walked to the crease in just his 11th first-class match, but was being Tweeted by Prime Minister Kevin Rudd as he wandered off.
Best also weighed in.
"I'm feeling your pain lad ... records are to be broken," the West Indian quick Tweeted.
"Must say we number 11 batters, in Agar and myself, love this English bowling attack. #SweetLikeSugarCane"
It was ridiculous in the extreme - right down to the rush-of-blood-to-the-head shot that cruelly denied him a remarkable century.
"What's the point moving the field Cooky? He's seeing it like a bloody size five football!" lamented a sunburnt English fan as Agar powered past 50 to a standing ovation.
By the time he'd entered the 80s, one small group of Australians, who had noted the silence around the ground, reprised a popular football chant.
"You're not singing anymoooooore," they bellowed.
Previously, when Australia lost 5-9 to be on the brink of a heavy first innings deficit, the hosts' fans had mixed celebratory cheers with derisive laughter.
But with dashing cut shots, audacious hooks, a pair of towering sixes and that unwavering smile, Agar shut them up and reserved his place in Ashes history.