Steven Fishman is, by all accounts, a very complicated person. His history, including his time in prison, is convoluted. But what I can say with a degree of certainty is that his lawsuit against Scientology was a milestone of sorts in litigation against the cult. The information brought in as evidence in the trial included the upper lever drivel concerning the OT levels along with various affidavits by former top Scientologists did a lot to shine the light on a group that would much rather stay in the dark. Anyway, here is what Wikipedia had to say on the subject:
What is an OT or operating thetan? It all started millions of years ago when the evil tyrant Xenu. Earth was a prison planet, I bet you didn’t know that. Heck, now it gets much better, go here for the full story. South Park did an excellent renditon of the tale.