He's a large mutant from the year 2066 who created a bunch of mutants to overpower the humans and destroy the city where he nearly took over the world. He appeared in Season Eight of the 1987 TV series, in three episodes: "Cry H.A.V.O.C.!", "H.A.V.O.C. in the Streets!", and "Enter: Krakus".
Krakus stated that Titanus is the most wanted criminal in his time. Titanus is not a good fighter and is easily defeated by the Turtles every time.
At the end of "Enter: Krakus," Donatello teleported him to the Dinosaur Age where he's last seen being chased by a large dinosaur and saying he'll get revenge on the Turtles if it's the last thing he does.