Who is Mark Renton from Trainspotting and what is their importance?

Mark Renton is the closest thing to a protagonist in Trainspotting. He is a young heroin addict living in Leith who alternately kicks junk and relapses throughout the novel. Before the narrative begins, Renton goes to Aberbeen University for one term before dropping out. He gets into smack more heavily after he disabled brother dies in hospital.