Forrest didn't have the most fights. But was a huge dog to shogun and rampage. 
KnowAnySailors -KnowAnySailors - Randy Couture:Oh! And Gabriel Gonzaga who was coming off THAT knockout.
He was 'supposed' to lose to: Chuck, Sylvia, Vitor, and Tito.
Thats who I was thinking. May not have the most, but hes who comes to mind when talking underdog victories. Joe Rogan , "thats why this man is my Hero"
dmjr98 -NoYousHerName -dmjr98 - Rashad. I think the one time he wasn't an underdog was against lil nog, every other fight INCLUDING the second fight with Ortiz he was supposed to lose.Lol you are trippin. He was not supposed to lose to Tito in their second fight, he was the betting favorite silly pantsUhhhhh are you sure? That was right after the bader fight and I remember everyone thought he was going to win.
Randy?
Vitor
Randleman
Rizzo
Tito
Chuck
Gonzaga
Tim
Those are all title level fights too. No one has defied the odds in big fights as Randy. Its not even close.
YousHerName -He was a huge favorite and Tito stepped up on short notice too didn't he?dmjr98 - Rashad. I think the one time he wasn't an underdog was against lil nog, every other fight INCLUDING the second fight with Ortiz he was supposed to lose.Lol you are trippin. He was not supposed to lose to Tito in their second fight, he was the betting favorite silly pants
Uni man -dmjr98 -NoYousHerName -dmjr98 - Rashad. I think the one time he wasn't an underdog was against lil nog, every other fight INCLUDING the second fight with Ortiz he was supposed to lose.Lol you are trippin. He was not supposed to lose to Tito in their second fight, he was the betting favorite silly pantsUhhhhh are you sure? That was right after the bader fight and I remember everyone thought he was going to win.
I was wrong about the odds. Rashad was the favorite in that fight. 
Lentz?
Would nick Newell be an underdog in all of his fights? Then him if so. I think he's won 11 fights
Def edgar. Hell he even lost a few that were actually wins as an under dog. Hes also prob my pick for most underrated fighter as well
Southpaw76 - Def edgar. Hell he even lost a few that were actually wins as an under dog. Hes also prob my pick for most underrated fighter as well
The most commonly repeated falsehood in MMA.
Frankie has lost 1 fight he actually won, the second Bendo fight, and has been given a gift win, the first BJ fight, plus a draw against Maynard. He is actually in the green.
Most people recognise Frankie as one of the best fighters P4P and if he beats Cub, he is back in with a chance for another title.
KnowAnySailors -KnowAnySailors - Randy Couture:Oh! And Gabriel Gonzaga who was coming off THAT knockout.
He was 'supposed' to lose to: Chuck, Sylvia, Vitor, and Tito.
I would have to agree. Randy's career was as constant series of him improving and changing his game just enough to beat whoever the next guy was.
You could watch him fight "X" and think "Y" would beat this guy, but when the fight actually came he had tweaked his game just enough to beat, or even humiliate, "Y", giving a performance that you just wouldn't have expected from him based on past fights.
Couture comes to mind.
He was all but written off over and over, only to rise to the occasion.
Forrest griffin vs rampage
Forrest griffin vs shogun
It feels like every time nick or nate Diaz win a fight, they're the underdog but I'm not sure if that's actually the case.