Darth Sethron was a 5000 year old Force Sensitive being from Mandalore. Much like. Darth Sion, Sethron relied upon using the Dark Side to hold his twisted and mangled body together. In his earlier life Sthron had trained five Apprentices. During the training of the fith Sethron had sensed the man's intention and had began studying the dark healing methods. When the Apprentice did strike Sethron down the Sith was able to use the Dark Side to hold his body together whilst his aide placed him in Stasis to be preserved.
During the Dark Times, Darth Zealot stumbled across Sethron's tomb and brought him out of stasis. Sethron joined Zealot in the attempt to defeat both Soru's order and Nihilus' Empire and began to teach Zealot the things Sion did not.
Quoting John Griffin
But...You made a mistake...
1; He is "Darth Sethron"
2; He is a 5,000 year old Jedi who turned Sith and was later killed by his 5th Apprentice.
3; He would be the sort of character who would try to kill Harash Soru and Darth Nihilus.
4; He belives that the only way to bring balance to the force is to kill the Jedi and Sith and make himself leader of the galaxy.
Plus...His name is 1;"Master Rezak Sethron" or 2;"Darth Sethron".
Sorry...but I had to correct you.~John