If we consider the very first UFC, held in Denver on November 12th 1993, as the true Ultimate Fighting Championship, there is a clear line of champions up until the present day.
Royce wen undefeated until May 1st 2000 when he lost to Kazushi Sakuraba in the very first Pride Grand Prix.
Sakuraba, then lost that same night to Igor Vovchanchyn, who then lost to the winner of the tournament Mark Coleman.
Mark Coleman would hang on to the lineal title for a little over a year until he faced Antonio Rodrigo Nogueira on September 24th 2001.
Nog would defend the title against 6 opponents until running in to one of the greatest fighters of all time, on one of the longest winning streaks of all time. Fedor Emelianenko would defeat Nog and take his title on March 16th 2003.
Fedor would then fight 10 opponents, finishing all but Mirko Filipovic, whom he would beat by decision. Fedor seemed unstoppable, and would have the lineal title until he retired. Until one day, seven years later. On June 26th, 2010, Fabricio Werdum took the title back to Brazil when he defeated Fedor by a Triangle Armbar just 1:09 in to the first round.
Werdum would not have the title for long, his very next fight, almost a year later on June 18th, 2011, Alistair Overeem would defeat him by unanimous decision.
Overeem would then goof around with Brock Lesnar, beating him by KO, then, last night, he would fall to Antonio Silva by KO just 25 seconds in to the third round of their fight.
Silva now reigns as the lineal Champion of the Ultimate Fighting Championship.
BUT while we are having fun with the title, let's take it a step further. Where would the title be if it could only be taken by KO or submission??
Royce > Matt Hughes KO 4:39 rnd 1
Matt Hughes > GSP Armbar 4:54 rnd 2
GSP > Matt Serra KO 3:25 rnd 1
Matt Serra > GSP KO 4:45 rnd 2
So GSP is the Lineal Champion if we only consider a stoppage as the true "defeating" of a fighter.