Tarantulas

Tarantulas is the cunning and treacherous scientist of the Predacons, who serves as the secondary antagonist of the CGI series ''Transformers: Beast Wars. ''He is one of the six original Predacons of Megatron's crew, who stole the Golden Disk before crash-landing on Earth along with the Maximals. His beast mode is a giant purple tarantula.

During the Beast Wars, Tarantulas is depicted as the Predacons' intelligent but insane scientist, spending most of his time away from his fellow Predacons and plotting his own agendas in his lair. When the Predacons intercepted a Maximal stasis pod, Tarantulas chose its beast form as a black widow spider, turning the protoform into the predacon Blackarachnia. Throughout the first season, Tarantulas repeatedly tries to betray Megatron and devise a way to escape Earth after discovering that mysterious aliens, known as "The Vok", were coming, even stealing a protoform's stasis pod to try and do so. In the season finale, a quantum surge transforms Tarantulas into a Transmetal.

In season two, it is revealed that Tarantulas is a secret agent working for the Predacon Alliance's Tripedicus Council, who consider Megatron a renegade. When the Council's lieutenant, Ravage, arrives on Earth, Tarantulas assists him in capturing Megatron. However, Ravage eventually releases Megatron after learning that he was following the instructions of the original Decepticon Megatron. But in the season finale, Ravage is killed and Tarantulas rejoins the Predacons.

In season three, Tarantulas continues serving under Megatron, but ultimately betrays him with the aid of Quickstrike. With Megatron subdued, Tarantulas reveals himself as a descendant of Unicron as opposed to Autobot or Decepticon, and attempts to destroy the Autobot ship, The Ark, to wipe out all the Maximals and other Predacons. However, he fails and once again leaves the Predacons to work alone. In the season finale, Tarantulas captures the Vok creation Tigerhawk, and attempts to override its programming so it will serve him. However, his machine extracted the Vok out of Tigerhawk's body, and they moved towards Tarantulas. Panicking, Tarantulas tried fired at them, only for his bullets to phase through them and hit his laser machine, causing it to turn and fire at Tarantulas, destroying both him and the Vok. Megatron later discovers that Tarantulas had discovered the location of the Decepticon warship, The Nemesis, resting on the ocean bed.

IDW comics
The Beast Wars: Primeval Dawn and Transformers: Universe comic lines have it so that Tarantulas survived his apparent demise, as the energy he absorbed from the Vok resurrected him. After waging a failed conflict with forces under the Maximal leader Primal Prime, he would join the forces of Unicron.

Trivia

 * Terrorsaur was originally intended to be the traitor seeking to overthrow Megatron as leader of the Predacons, but Tarantulas soon revealed himself as a far greater threat to Megatron's rule, being more treacherous and intelligent than Terrorsaur ever was. Thus, the writers killed Terrorsaur off at the end of season one, and Tarantulas became the only traitor remaining in Megatron's midst.
 * Tarantulas seems to be an amalgamation of the Decepticons Starscream and Shockwave; He shares Starscream's treachery, ambition and cowardice, but also has Shockwave's intellect and technological skills. In addition, Tarantulas' appearance is similar to Shockwave as well, in that he is predominantly purple, and has one singular eye, although in Tarantulas' case it is a visor as opposed to Shockwave's cyclops-like optic.
 * According to the stats of the Beast Wars toys, Tarantulas is the only Transformer from the series who scored a maximum 10 out of 10 for Intelligence, making him the smartest character in the show.
 * Tarantulas has been trying to destroy the Vok for most of the series. In the end it is he who destroys them, but is killed along with them.
 * Like Terrorsaur and Scorponok, Tarantulas was killed in the TV series and survived this in the comics (which may be non-canon). IDW has also done this with the My Little Pony villains Queen Chrysalis (though it is debatable whether she is dead in the show) and King Sombra (who returned as a ghost and was resurrected in the comics).