#1 Keith Hackney
Keith Hackney made his UFC debut way back at UFC 3 in September of 1994. Pitted against the enormous 600 Ibs Sumo star, Emmanuel Yarborough, the much smaller Hackney understandably was an underdog.
Giving away 350 Ibs in weight, the fight appeared to be a mismatch. That looked to be the case when Yarborough mauled Hackney and sent him careering out of the Octagon door.
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Hackney responded by using his speed to dodge any further attacks and picked his spot and floored Yarborough with a big right hand and then finished him off with a spectacular flurry of punches which caused him to injure his hand and withdraw from the UFC 3 tournament.
Hackney made his return against another giant at UFC 4, the fearsome Joe Son (who would later be convicted of murder and numerous other felonies) in a fight infamous for the "Giant Killer" pounding Son's groin repeatedly before earning a submission win.
His brief UFC career ended with consecutive defeats to former UFC Tournament winners, Royce Gracie and Marco Ruas. His final fight in the promotion occurred on December 16, 1995.
23 years later, Hackney's short-lived career seldom gets any airtime in UFC which is a shame as his impact at the early UFC events was vast.