Further down the ICC list is Yasser Seirawan, aka Om (as in the Hindu mantra?), another former U.S. Champion. He last played in November 2013, and was last featured on this blog in A Few More Chess960 Resources.
Ranked just beneath Seirawan is Fabiano Caruana, aka Adaptation, and, like Nakmura, another world top-10 player at traditional chess. I wasn't aware that he was a chess960 player until I wrote the 'Top ICC' post. He last played in July this year.
While I was writing this current post, I discovered two active players who don't feature on any 'best' list but who might be important to the history of chess960: GM Miguel Quinteros, aka mquinteros, and GM Eugene Torre, aka Bradidik. Both are known to have been friendly with Fischer. Did they ever play his invention with him? I hope that some day we find out one way or the other.