Conaway is best known to most people from his roles in the TV series Taxi and the movie Grease. But to SF fans, he will be warmly remember for his role as Zack Allan on Babylon 5. I recently finished re-watching the whole run of B5, and was once again impressed with both the character and with Conaway's portrayal.
Conaway struggled with drug abuse and addiction for much of his life. (Knowing this lends quite a bit of pathos to a scene in an episode of Babylon 5 where he confronts an alcoholic friend about relapsing.) In recent years he had been put through the exploitation of VH-1's Celebrity Rehab and subject to the bullshit of the "Church" of Scientology. Perhaps if he'd gotten genuine help, things could have gone differently; but instead, on May 11, Conaway collapsed from use of painkillers and prescription drugs, and was hospitalized with pneumonia and sepsis, which eventually proved fatal.