Mattson was an articulate prisoner of Persephone in Rapture who spoke with a Cockney accent. He was held in Cell Block D. Like most all of the inmates, Mattson could no longer stand the intolerable cruelty inflicted upon him, and planned to escape by causing a riot. He figured out Warden Nigel Weir's code to the security booth and had a Hack Tool which he planned to use on the prison's security Turrets and bots. Apparently, he never succeeded, as his tape was interrupted right before completely saying the code into his Audio Diary.