Seth is the final boss of Capcom's Street Fighter IV.
Seth is also known as "The Pupper Master." He is the head of Shadowloo's weapons division, S.I.N.. He has augmented his body with bionic parts to maximize his fighting potential.
According to David Crislip, the Assistant Producer of Street Fighter IV, on the Top Secret Bionic Commando Podcast: File 032, Seth's name comes from the story of Kane and Abel; Seth being the name of the obscure third brother of Kane and Abel. This has to do with a connection between the last boss and the other SF IV character Abel They were going to name the last boss Kane, but this name had already been used for a last boss in the game 'Mark Of The Wolves". David Crislip also notes that they had the added bonus of telling people that they named the boss after Seth Killian, who works at Capcom USA and is known for his Street Fighter prowess.