From a post by Helwig on the UG
Cain in fact posseses the FIFTH version of the UFC HW title.
This title is one that was made following the motorcycle accident of Frank Mir. Afterwards, the man Mir had just defeated for the belt in Tim Sylvia, faced the #1 contender in Andrei Arlovski, to fight for the injured Mir's title.
Mir's title(the 4th version) was won from Sylvia, who himself got it off of Ricco Rodriguez.
Ricco got it not by beating the HW champion, but by beating the former HW champion in Randy Couture.
Barnett had beaten Randy for the belt(3rd version) but tested positive for steroids. So while blackballed and stripped of the belt, the results were not overurned and declared a NC. Barnett left and retained the UFC HW title victory.
That title that left with Barnett had a decent shelf life going back to Randleman vs Williams. Neither was the champ at the time but Bas Rutten had won and then immediately retired with the belt(2nd version) So they had to create a new belt to continue with.
The original title was removed when Randy left as the UFC HW champ in 1997 and then started losing in Japan. It linearly is passed almost exclusively through the hands of the best fighters and #1 ranked champions until it presently winds up with Werdum
In summary:
1st UFC HW title: Coleman-Smith-Couture-Inoue-Kerr-Fujita-Coleman-Nog-Fedor-Werdum
2nd UFC HW title: New tournament pits Rutten against Randleman. Rutten wins and immediately retires. Defends one time, 8 years later against Warpath.
3rd UFC HW title: New tournament pits Pete Williams against Randleman. Randleman wins. Couture comes back as the last man to hold the original UFC title in the UFC(to this very day) and takes it. Couture eventually loses to Barnett. But Barnett tests positive and leaves the UFC, with he belt.
4th UFC HW title: Former champ Couture fights Ricco Rodriguez. Ricco wins. Tim Sylvia takes out Ricco. Mir takes out Tim Sylvia. Mir is then in a horrendous auto accident and cannot fight indefinitely so he is stripped of the belt.
5th UFC HW title: Former champion Sylvia fights Arlovski for the new belt. Arlovski wins. Sylvia wins it back. Couture comes back yet again as the last man to ever hold the original UFC HW title in the UFC(to this day) and wins. Couture loses to Lesnar. Lesnar loses to Cain.
Thats where we are now.