Thistleclaw

Thistleclaw was a warrior ready to become deputy when Tawnyspots retired (much like Bluefur was). He was strong and brave, but his answer to every problem was to fight. According to Bluestar, he would've forced the Clans into unnecessary wars. He didn't become deputy because Bluestar did. Wild and arrogant to the last, she couldn't let him destroy ThunderClan. He died during a RiverClan raid shortly before Firepaw joined ThunderClan.

Secrets of the Clans
In Secrets of the Clans, former ThunderClan leader Owlstar says that if Bluestar had stayed in the nursery with her three kits, Thistleclaw would have become deputy. Owlstar also asks other StarClan cats who would have wanted to see more cats joining StarClan because of the battles Thistleclaw had started.