To me, without Angelo Drossos, there is no Spurs.
It might have been easy, in 1976, for Drossos to take the money and run. He could have simply sold out and allowed a different ABA team to be part of the merger -- the owners of the Spirits of St. Louis did exactly that. But he didn't and ended up giving San Antonio the gift that keeps on giving. Beyond that, Drossos became a steward to the needs of small market teams and, through his efforts, ensured that a team could stay in San Antonio and be viable (at least on the court) because of rules that level the playing field. In the years that have followed, the franchise that he created has been able to develop a culture of winning, manifested by its 4 championships, its 10 appearances in the conference finals, and its 15 division crowns and 28 playoff appearances. More than that, even, the consistency of the operation that Drossos made happen is evidenced by the fact that his team has the 2nd best aggregate winning percentage in NBA history and the 2nd most playoff wins of all franchises since the merger. All of that from a team that operates in one of the smallest markets in pro sports, in an era in which the disparity between big markets and small is greater than ever.
To be sure, the Spurs have been fortunate in a number of ways that have made all of the above happen. But none of it would have been possible without Drossos and other than the 3 superstars who've toiled for the franchise and have made the Spurs viable on the court, I can't imagine that anyone has truly been more important to the Spurs' history than Angelo Drossos.
No Drossos, no Spurs.