This show is a resurrection of a podcast of the same name, also hosted by Sam Riegel and Liam O"Brien. The podcast was originally a way for the friends who both have families, to make time to get together and hang out.
Critical Role originally started out as a one-off DnD game for Liam's birthday, that came about as a result of Liam's interest and was talked about on the podcast before either All Work No Play, or Critical Role became a TV show.