Arvydas Sabonis.
This. I don't even think it's close. Prime Sabas was a GOAT candidate in my book. If he had entered the NBA in his late teens/early 20s, I bet he would have been in the same convo with Kareem/Wilt/Russ/Dream/Shaq. Talent-wise, I think he was better than all of them. The way I see it, he was a rich man's Jokic. No disrespect to the brilliance of the Joker, but I fully believe prime Sabas was hands down the better player. Likewise, I think Jokic is a rich man's prime Walton (although Walton was definitely a better rim protector).
A couple more names:
Magic. If it weren't for the HIV diagnosis, I believe he would have had a better GOAT case than Jordan. Personally speaking, I consider him the GOAT regardless, but I realise he doesn't have the longevity of some of the other candidates.
Drazen. Imo, he was the first Steph Curry. Most elite shooters are off-ball specialists (for instance, Klay, Reggie). Drazen was a god-level shooter who could also put the ball on the floor and create his own shot. Steph is a better ball handler/facilitator, but Drazen was 3 inches taller, hence he was better at creating his own shot, especially in the clutch. He was also a ruthless competitor who thrived under pressure. The only player ever who wasn't afraid to regularly talk trash to prime Jordan and could actually back it up.