Who is the fighter that had the most potential but never prospered. To me it is Joe Daddy, it seems like he could have done so much after the loss to B.J he just fell off though 
Stevenson was a pretty solid fighter before Tuf imo.
Off the top, my list goes-
Arona
Guy Mezger
Rulon Gardner
Todd duffee
Forgot to add. Could B.J. Penn go on the list even though he has many credentials? If so I believe he is number 1
freddy adu
wilson gouveia.
he had a stretch of 6 - 1 with 6 finishes in the ufc. in the marquadt fight, he seemed ill prepared, and has not found his old form since then.
billcosbiguez - wilson gouveia.
he had a stretch of 6 - 1 with 6 finishes in the ufc. in the marquadt fight, he seemed ill prepared, and has not found his old form since then.
Does gouveia still fight?
It's Vitor and there's not a close second.
JESSE TAYLOR
and Drew Fickett
and I always thought that Joe Riggs was going to hold the strap. He proved me wrong
Marcelo Garcia was all upside in MMA, but for varios reasons never got his MMa career going.
Which is a shame, because I love his grappling style as well as his training ethic.
MmaLovesMe -billcosbiguez - wilson gouveia.Does gouveia still fight? <img src="/images/phone/apple.png" alt="Phone Post" border="0" style="vertical-align:middle;"/>
he had a stretch of 6 - 1 with 6 finishes in the ufc. in the marquadt fight, he seemed ill prepared, and has not found his old form since then.
he recently won in mfc after losing a few in mfc.
MmaLovesMe -billcosbiguez - wilson gouveia.Does gouveia still fight? <img src="/images/phone/apple.png" alt="Phone Post" border="0" style="vertical-align:middle;"/>
he had a stretch of 6 - 1 with 6 finishes in the ufc. in the marquadt fight, he seemed ill prepared, and has not found his old form since then.
he recently won in mfc after losing a few in mfc.
Pure - It's Vitor and there's not a close second.
her has prospered, but people expected him to be fedor-esque or a silva-esque. it's tough to live up to those expectations.
Robbie lawler
I might get flamed for this but...
Genki sudo.
He is one of my favorite fighters of all time and he achieved a lot but he won't go down as one of the all time greats and I think he could have. He should have beat Ludwig and he probably would have gone on to win the UFC lightweight title. He retired too early and was ahead of his time.
Seemed like the sky was the limit for Karo and instead of putting it together he just dropped sharply.
You HAVE to mention Arlovski
Stephen Bonnar 
MmaLovesMe - Who is the fighter that had the most potential but never prospered. To me it is Joe Daddy, it seems like he could have done so much after the loss to B.J he just fell off though
II met him in 06 at UFC 57. I was so suprised at how short he was. He couldnt have been more than 5'5'
Hands Down Roy Nelson, The man could easily be an extremely talented LHW even MW, tighten up that power right with solid combinations, USE that blackbelt in BJJ, and enjoy the chin instead of testing it.