Susan "Mandark" Astronomonov is the evil rival of boy genius Dexter and would-be love-interest of Dexter's bubble-headed older sister Dee Dee on the Dexter's Laboratory series. According to Mandark himself, he and Dexter have been competing in science and other things for years, but he tries to win "by being sneaky and bad." Mandark is arrogant and childish in nature, but has on occasion teamed up with Dexter to combat a greater danger. Mandark is well known for his distinctive laugh: "Haaaa hahaaa! Haaa haha haha!"
The nano enemy of Dexter who joined the battle against Lord Fuse.