Memos at UCLA confirm that Shatner had 5% profit participation in Star Trek, at least in 1965 (I have no idea how his 1969 divorce may have affected this percentage, for example). Page 500 of David Alexander's Roddenberry biography details how Shatner and Roddenberry successfully pressured the studio into paying up for the first time after threatening an audit in 1986. Roddenberry's portion of the profits at the time was $851,000; Shatner's portion would have been less than that.
In other words, valuable, but not hundreds of millions of dollars valuable.
Shatner was able to hold onto his stake in ST? I wonder where I heard otherwise. There's a lot of bull on the Internet, it turns out, and I picked some of it up. Somebody really should fact check the subject!
