Taransu
Taransu was the "mad scientist" of the Destrons, he was actually a mole planted by the Tripredacus Council, in the hopes of subverting Megatron's plans. However, upon his arrival on prehistoric Earth, Tarantulas began to follow his own agenda. He designed a variety of advanced weapons and technology for Megatron, as well as the shell program that enabled Cybertron protoforms to be reprogrammed into Destrons. Using it, he was responsible for the creation of Black Widow and Inferno. However, despite his seeming loyalty, he still pursued his own goals. He built an independent lab away from the Destron ship, the Darkside- however, this was later destroyed.
During the events leading to the quantum surge, Taransu attempted to leave the planet using a transwarp cell and a modified stasis pod. Black Widow assisted him (with plans of betraying him and taking the ship for herself), but before he could finish, he was taken down by Inferno. When Black Widow tried to download his data tracks using a cyberlink, so as to gain the knowledge she needed to finish the job, Taransu's mind entered her body. The two shared that form until after the surge had passed. He was subsequently restored to his body, which had been transformed into a Transmetal, but maintained a virtual cyberlink to Black Widow, allowing him to monitor and influence her actions.
When Taransu took himself, Black Widow, and Quickstrike to operate on their own in a secret base, the distaff Destron used the energies of a cube of energon to force him to break the link. He was enraged, but Cybertrons Silverbolt and Rattor attacked and seemingly destroyed the hideout before he could do anything. He told Megatron that the station he'd purported to be building was destroyed, but in reality he'd made it his new lair.
Taransu seceded from the other Destrons after that point, though he did aid them in a few campaigns that coincided with his goals. Taransu made one final significant attempt at insurrection- when Megatron attempted to increase his power by integrating the original Megatron's spark into his own, he had Quickstrike dunk him in lava. However, this did not destroy Megatron- instead, he arose as a powerful dragon, and severely damaged Taransu before leaving.
He retreated to his lair, and when the mighty alien amalgam, Tigerhawk, arrived, he captured it and planned to use it to destroy the Ark. Before he could do this, Tigerhawk's creators, the Vok, destroyed him. His last legacy was an attempt to reconstruct the Destron warship, the Nemesis.
Taransu's original beast mode was that of a spider- his Transmetal body could transform into a mechanical spider or a motorcycle-like vehicle.
