The Titan Robot was created by Cyborg in the episode The Left Leg for extreme missions that require the use of all five unified Titans.
Powers and Abilities
The guitar riff that plays when the titans are about to go down the chutes to the robot sounds similar to one of the main riffs in the theme song to Mighty Morphin' Power Rangers.
The fact that Robin pilots the left leg could be a reference to Devastator from Transformers: G1 because Scrapper (the leader of the Constructicons) transformed into the right leg.
The robot may be inspired by the Power Rangers, who would use a robot, the megazord, to take on giant versions of the monsters they battle. this is justified by the fact that most teams of rangers are composed of 5 members.