Series co-creator Alec Berg thought that a show about a hitman wouldn't be well-received or funny, until fellow co-creator, Bill Hader, asked "well, what if the hitman was me?"
While filming his final scene of season two, Henry Winkler looked around between takes and realized that they were filming on the same soundstage where he had filmed "Happy Days" over forty years earlier. The entire cast and crew became distracted while Winkler walked around the stage and pointed out where specific locations and sets had been constructed.
Henry Winkler showed up to audition for the show. Bill Hader and Alec Berg have stated that they would have just offered him the role regardless, but Winkler insisted that he audition like everyone else.
Bill Hader developed the show with Alec Berg after getting a development deal from HBO. HBO offered Hader the development deal after seeing Hader's performance in The Skeleton Twins (2014).