Jenner

Jenner is the main antagonist of the 1982 animated adaptation of Mrs. Frisby And The Rats Of NIMH, known commonly as The Secret Of NIMH, he is a rat who betrayed his own kind due to his desire to remain in the rose bush, rather than leave to a better life in Thorn Valley, like promised by the elder leader Nicodemus.

Role
Jenner first meets Mrs. Frisby when she comes to the rats for help to move her home. Jenner concocts a plan on the spot and immediately voices his support to help move the Frisby home under the impression that it would honor the late Jonathan Brisby. Mrs. Frisby politely thanks Jenner but is clearly uneasy in his presence. As Nicodemus and Mrs. Frisby are leaving for their boat ride, Jenner carefully explains his plan to his confidant Sullivan; his plan is to sabotage the operation by cutting the ropes that will be used to lift and move the Frisby home in the hopes that it will crush Nicodemus. Sullivan expresses reluctance to taking such a risk and when he asks what to do about Justin, Jenner simply replies "Leave him to me."

During the moving of the Frisby home, Jenner and Sullivan stand ready to cut the ropes. The cement block house comes to hover directly above Nicodemus and Jenner cuts the lines on his own. Sullivan takes no part in cutting the ropes after having second thoughts. Nicodemus is subsequently crushed by the heavy equipment, while the block lands in a mud puddle.

With Nicodemus dead and the rats fallen into grief, Jenner uses the situation to declare himself as the new leader and persuade the others to return to the rose bush. Mrs. Frisby arrives during his speech and frantically warns the rats that NIMH will arrive in the morning to destroy the rose bush and any rats living within. Jenner attempts to discredit her saying she has become hysterical, but the rats believe her and decide they must leave. Enraged by her meddling he attacks her with the intention of killing her. Sullivan alerts Justin to the attack, causing Justin to throw himself between Jenner and Frisby. As Brisby recovers from the initial violence Jenner spots the necklace of power given to her by Nicodemus and moves to attack her again. Justin tries to stop him but thrown aside and wounded by Jenner. Jenner tackles Frisby as she's running away and violently manhandles her trying to get the necklace. Justin comes to her aid and the two rats engage in a sword fight right after Jenner slashes Sullivan across the neck, mortally wounding him. Jenner then continues his fight with Justin, finally revealing that he killed Nicodemus, and is stabbed in the stomach by Justin. As Justin makes his annoucement to the colony, Jenner sneaks up behind him atop the stone and prepares to kill him from behind while Sullivan, who is dying, takes out a dagger. Elizabeth gasps in terror and points up towards Jenner to warn Justin. Before Jenner can attack, Sullivan delivers the fatal blow to the nefarious rat, throwing his dagger striking Jenner in the back and sending him over the stone to his death.

Jenner was voiced by actor Paul Shenar, who portrayed the Bolivian drug lord Alexander Sosa (Scarface, 1983) and womanizer Alexander Cross (The Mask of Alexander Cross, 1977)

In the Graphic Novels - Jenner plotted to have Revenge on Mrs. Frisby and Justin after Dragon the Cat found him outside the Farm.