Okay, thinking it's about time to nominate KG and so I'll tell my personal story about him that cemented him as my favorite basketball player forever.
I attended a small liberal arts college in MN in the early 2000s. During that time, the Timberwolves did their preseason camp there and timed it for what I assume was our fall break (because the campus was basically empty except for student athletes and those of us from out of state who didn't go home). While I wasn't on the basketball team, my roommate was and I was good friends with a lot of the guys from pick up or whatever. The college team effectively worked as security for the closed practices and the school's gym windows were generally blocked from public view. This is important to note because it meant that the practices were effectively closed to the outside world but for the Timberwolves employees and a few of us associated with the college basketball team that got to sit in and watch (provided we didn't interrupt anything).
Now, again, these were closed practices and the camp before the actual preseason or whatever even started - so no fans, media, etc. So, a lot of the regular players (Sprewell, Terrell Brandon, Cassell, Joe Smith, Wally, etc.) who didn't have to really make the team utilized the practices to rehab their bodies or work on particular skills or whatever. To be clear, the players weren't screwing around and put in their respective work, but it was pretty clear that most of the guys approached the camp as a necessary evil and did their work and counted their days until they could go back down to the cities and their homes. Put it this way, Iverson would have not tried very hard.
But KG? In this preseason camp, with nobody looking, his spot obviously secure, and really nobody at all to impress, KG still took on each moment like it was game 7 of the NBA finals. With Flip Saunders usually off working individually with some guys or milling around with coaches, KG ran the practices himself with sheer intensity. Particularly, he tried his best with Ndudi Ibi (who just wasn't ready to be there, frankly, and was terrible - I even watched him air ball a layup to KG's utter dismay) and spent much of the time working with him. There was obviously mutual respect with him and guys like Cassell (who, bizarrely practiced in sweatpants), Sprewell (fun dude), Mark Madsen (dude had a serious energy level) and Wally (aloof but **** he could shoot) but it was abundantly clear who ran this team and it wasn't Flip or McHale. After practice the players would use our weight room (which was still open to us students) so I timed it each time to lift at the same times and KG was just as intense in the weight room with nobody watching (though I distinctly recall his dumbell curl form being terrible). And, thereafter, when most of the other players would throw on hoodies and get out of there as quickly as they could to the team vans, KG would go outside and, even though he totally didn't have to, sign some autographs for the locals who knew of the practices and give up 15 minutes of his day to do so when he didn't have to at all.
I have had the opportunity to encounter a good number of other professional athletes - whether in their sport or on the golf course - and never met any one who sniffed at KG's drive, intensity, and sheer love for what he was doing. Still impresses the hell out of me to this day because, after all, we be talking about just a [closed] practice. And, for that reason, he gets my biased nod for being a top 20 guy of all-time and not even
@SWC can hold me back on this one.