Dark Clank is Clank after he is experimented on with Dark Matter. Surprisingly, Clank was experimented on before Ratchet. The robots Infernox sent out to capture heroes only got Ratchet. When they found out Clank had followed them, they did horrible things to Clank. When Clank changes into Dark Clank, he changes into Alpha Clank and then his eyes go red and parts of him get neon-like properties. He can run at 5x his normal speed and jump 3x higher than normal. Unfortunatly when Clank goes into his Dark Form, he can't use the heli-pack, thruster pack, hydro pack, etc.
Books where Dark Clank is seen:
-Ratchet & Clank: The Return of Dreadzone
-Ratchet & Clank: The Dark Lombaxes
-Ratchet & Clank: The Final Chapter