Serious characters who later became jokes/losers
Recently I was looking at the original Champion (Elder of the Universe) appearance and how different he was to what he became later on. He started out as a deadly, unbeatable and honorable fighter and seemed reasonably intelligent as well.
Later (perhaps around the time of Thanos Quest) he became a brutish idiot, and later still he just seemed to be a bit of a joke, with characters like She-Hulk beating him.
It's kind of hard for characters to recover from such treatment.
It made me wonder - what other characters out there were introduced as serious characters, but had later writers turn them into jokes or complete idiots despite contradicting the earlier appearance(s)?
I know there are more (especially among the villains) but I can't think of any offhand...