Johnson originally auditioned for the role of ill-fated Terry Crowley in "The Shield", which ultimately went to Reed Diamond. Casting directors were so impressed with his audition that they asked Johnson to come in for the role of Curtis Lemansky. He was unsure of how to go about the character, as the role was not very developed at that point. During the audition, Johnson made some choices for the character that he initially thought ruined his chances of winning the role. However, the audition turned out to be successful and he was cast. Lemansky quickly became a major player in the first season because of the chemistry Johnson shared with his castmates.