Styx has changed over time, with people in and out for their own reasons, etc.  I've listed everyone, what they played on average, and their times roughly of when they were a part of Styx. Each name links/will link to a page with some thoughts from me about them. [When I say Vocals, I mean lead-type.] Styx started in the early 70's with their first album in 1972, so start means that.

Dennis DeYoung - Keyboards, Vocals [start -> 1999]
James Young - Guitars, Vocals [start -> present]
John Panozzo - Drums, Percussion [start -> 1996]
Chuck Panozzo - Bass Guitars [start -> present {Chuck is there, but not as much}]
John Curulewski - Guitars, Vocals [start -> 1975]
Tommy Shaw - Guitars, Vocals [1975 -> 1984, 1995 -> present]
Glen Burtnik - Guitars, Vocals (Bass Guitar) [1989 -> 1995, 1999 -> present]
Todd Sucherman - Drums, Percussion [1996 -> present]
Lawrence Gowan - Keyboards, Vocals [1999 -> present]