Two quotes/incidents really sum him up for me.
Rob Symth in the Guardian about Pakistan drawing in three series' with the legendary WI team of the 80s with Imran ensuring it by batting five hours out in his last ever test:-
"It was fitting that the last word went to Imran, because he lorded over these contests like a colossus. Despite a series of ailments he was Pakistan's only ever-present in those three series (West Indies had five). Nobody on either side got near his 45 wickets at the blistering average of 14.87, and he added 356 runs at 32.36 for good measure. At the age of 38, this was his last significant act in Test cricket. He could retire safe in the knowledge that he had not lost the final battle, and that he had never lost the war."
Wasim Bari wrote about a chat he had with the Manager of the Indian team, The Maharaja of Baroda before the 1982-83 series in Pakistan. The Manager said "We have a batting line-up, till No. 11, and nothing can go through them." Bari replied "You haven't seen Imran yet because even if you have 15, he'll go through you."
The rest as they say is history, as Imran famously decimated the Indian Order in the second Innings for 8-60 in perhaps the finest display of reverse swing ever and went on take 40 wickets @ 14 for the series in some of the flattest Indian pitches you'd see with no other bowler in both sides coming anywhere close.
What I find most amazing is that even going beyond his prima facie mind blowing stats, He raised his performance to unbelievable levels when the odds were against him. Imran is one of the 3-4 pacers who'd make my list on bowling alone. I'd have him at #2 after Bradman if I made a list. Completely well deserved.