Off the top of my head I don’t remember how much the book of #Dune talks about the Harkonnen use of gladiatorial combat, but the movie draws a relatively subtle link between their idea of it and bullfighting - the guys in the wide black hats are like picadors, who stab the bull with lances to weaken it. I’ll avoid spoilers on a 60-year-old book or the new movie, but it’s a fun subtle thing.
I think Herbert mentions how Leto’s father died fighting a bull, but that’s about it, unless that comes up in books after the first. I need to read Messiah, which is conveniently next on the list after #InfiniteDetail.