Jenner . In Pooh's Adventures of The Secret of NIMH to do this, he called Giovanni to send over Team Rocket to aid his evil scheme. Although he managed to kill Nicodemus, Jenner was killed by Sullivan by having a knife thrown to his back during his battle with Justin. In The New World of the Furlings: Woody Woodpecker To The Rescue. Jenner Kidnaps Princess Odette Just To Make Her Queen!
Jenner first meets Mrs. Brisby when she comes to the rats to ask for help moving her home. Jenner concocts a plan on the spot to use this as an opportunity to get rid of Nicodemus; the leader of the rats whom he openly disagrees with. He immediately voices his support to help move the Brisby home under the impression that it would honor the late Jonathan Brisby. Mrs. Brisby was uneasy in Jenner's presence, but thanked him anyway. As Nicodemus and Mrs. Brisby are leaving for their boat ride, Jenner carefully explains his plan to his confidant Sullivan; to sabotage the operation by cutting the ropes that will be used to lift and move the Brisby 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; the head of the rat guards, Jenner simply replies "Leave him to me."
During the moving of the Brisby home, Jenner and Sullivan stand ready to cut the ropes. The cement block house comes to hover directly above Nicodemus and Jenner cuts one of the lines. Sullivan decides to take no part in cutting the ropes after having second thoughts about killing Nicodemus. Furious, Jenner rushes forward and cuts the rope himself, dropping the Brisby home, and killing Nicodemus.
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. Brisby 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 Brisby. As Brisby recovers from the initial violence, Jenner spots the necklace of power given to her by Nicodemus and moves to attack her again, desiring the magical item for himself. Justin tries to stop him, but he is thrown aside and wounded by Jenner. Jenner tackles Brisby 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. While they are dueling, Justin (having been fully aware of Jenner's growing resentment and animosity toward Nicodemus, coupled with having seen Jenner fly into a homicidal rage, attacking innocent creatures) correctly deduces that Jenner must have intentionally killed Nicodemus. Jenner does not even attempt to deny this, openly admitting to Justin that he killed Nicodemus, stating "I've learnt this much; take what you can, when you can!" and only stops fighting when he is stabbed in the stomach by Justin. As Justin makes his announcement to the colony that they were going to leave the rose bush, Jenner sneaks up behind him atop a large 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, however, Sullivan delivers the fatal blow to the nefarious rat, throwing his dagger which strikes Jenner in the back, causing him to fall over the stone to his death.
- Jenner was voiced by actor Paul Shenar, who portrayed the Bolivian drug lord Alejandro Sosa (Scarface, 1983) and womanizer Alexander Cross (The Mask of Alexander Cross, 1977)
- In the Graphic Novels - Jenner plotted to have Revenge on Mrs. Brisby and Justin after Dragon the Cat found him outside the Farm.
- Jenner is somewhat similar to Scar from The Lion King: They both had black fur, they were first in line to be the next ruler until they were upstaged by the male leads (Jenner: Justin, Scar: Simba), both used the female leads as pawns in their plans, (Jenner: Brisby, Scar: Nala), commited tragic murders to the old rulers and claimed it to be an accident, (Jenner: Nicodemus, Scar: Mufasa) and got dispatched by their henchmen. (Jenner: Sullivan, Scar: Hyenas).
- In the novel Mrs. Frisby and the Rats of NIMH, Jenner a minor character. He is not seen, except in a flashback narrated by Nicodemus. In the novel he begins as Nicodemus' friend during the rats' escape from NIMH, but starts to grow apart when he opposes Nicodemus' plan to leave the farm and live independently. Jenner prefers to stay on the farm and slowly drive the humans out. Eventually he leads a splinter group of rats away to start their own colony. Later it is heard that a number of rats were found electrocuted in a hardware store, but whether or not this is Jenner's group is uncertain.
- Jenner will become the main villain in Littlefoot's Adventures of The Secret of NIMH.
- Jenner will become the main villain in Aladar's Adventures of The Secret of NIMH.
- Jenner will become the main villain in Danny and the Secret of NIMH.
- Jenner will get his revenge on Littlefoot and his friends in Littlefoot Goes to FernGully: The Last Rainforest.
- Jenner will become the main villain in Logan and The Secret of NIMH.