Martin Brisby is the hidden main antagonist in The Secret of NIMH 2: Timmy to the Rescue. He did appear in the first Secret of NIMH film, but he wasn't villainous then, so that doesn't count. Instead, this is about when he was a villain in the sequel.
Martin is Timmy's brother and son of Mrs. Brisby. He was captured by NIMH. He became insane when the doctors brainwashed him. After being made insane, Martin took over the lab and brainwashed Dr. Valentine with a device similar to the one Valentine used on him and made him think he was a dog. Martin plans to use an army of lab rats riding a flock of ravens to take over Thorn Valley.
He asks Timmy to join him, but he refuses and is locked in a cage as Martin drags Jenny away to try to make her his queen. Timmy escapes with the help of Cecil and they go to free Jenny. Together, they knock out Martin and Timmy tricks Martin's army of ravens and rats to fly in the wrong direction. Timmy and Jenny then leave to find the others, only to find once everyone is free that NIMH is on fire. The survivors (Timmy, Jenny, and her parents, as well as Justin and Brutus) flee. Timmy goes back to save Martin. Before he leaves, Jenny tells him she loves him and he tells her the same. After being attacked by the cats Muriel & Floyd once again, Timmy sends them down an elevator shaft and finally finds Martin... actually, Martin finds him.
Timmy and Martin are able to escape through the lab's skylight, with some help from Jeremy. Jeremy takes the survivors to safety. The mice return to Thorn Valley, and Martin returns to normal.
- Despite the fact that he was brainwashed by Dr. Valentine, Martin is the main antagonist of the film because he had bigger plans than anyone else.
- In the second film, Martin is voiced by Eric Idle.
- Martin is similar to Rex Lewis from G.I. Joe: The Rise of Cobra, because they used to be good people before they were brainwashed by evil corporations, which caused them to turn evil and wrest command from the leaders of their respective organizations.