American film and television actor is best known to the audience for portraying Man in Black, the main antagonist in the Emmy Award-winning TV series Lost. Since starting out in showbiz in the 1990s, he has worked primarily in television, and has appeared in shows like NYPD Blue, Star Trek: Voyager, Deadwood, The Good Wife and the police procedural Bosch, the last of which features him in the titular role.

Besides his extensive body of work in TV, Welliver has also acted in over 25 films. Significant among these are the action thriller Assault on Precinct 13 (2005), the neo-noir mystery drama Gone Baby Gone (2007), The Town (2010), the Academy Award-winning historical drama Argo (2012) and the sci-fi action film Transformers: Age of Extinction (2014). Notable acting credits in recent times include Live By Night (2016) and the action film Escape Plan 2: Hades (2018), which starred Sylvester Stallone and Dave Bautista in the lead roles.