Jenner is a member of the Villain League and is the main villain from Spyro's adventures of 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.

When Mrs. Brisby, or as fans call her Elizabeth (in dedication to the actress who voiced her and shortly died of suicide.), comes to get the Rats' help, she is introduced to the council, which Jenner is in, by the Captain of the Guard Justin. Jenner decides to use the widow's help as part of his plan to kill Nicodemus. Elizabeth becomes frightened by Jenner when he takes her hand and almost reaches her closely by the nose. Then later, as Nicodemus and Elizabeth are leaving for their boat ride, Jenner carefully explains the plan to Sullivan; he'll cut the rope, thats attached to the house, and then the weight will crush him to death. After he kills Nicodemus, he'll become the new leader.

That night, during the moving of Elizabeth's home, Jenner and Sullivan wait ready to cut the rope. When the cinder block comes midway, Jenner cuts the lines on his own without Sullivan, because he turned against him. Instead of the cinder block crushing Nicodemus, he was killed by the weight of the equipment, which was a pulley.

As the process of the plan continues, Jenner then uses the situation to get the other rats to his cause, making it out as a terrible accident. However when Elizabeth interrupts with warning about NIMH arriving, Jenner grows enraged and attacks her. Justin runs between him and Elizabeth; but when the Stone glows, Jenner's interest grow among Elizabeth's stone. Justin tries to stop him, but Jenner slashes his left arm. Then he jumps off the house and jumps on top of Elizabeth and begins to strangle her as she tries to break free from his frightening strong grip. This forces Justin to come to her aid and the two rats engage in a sword fight right after Jenner slashes Sullivan across the stomach, brutally wounding him. Jenner gets stabbed in the stomach by Justin, but doesn't die. As Justin makes his annoucement to the colony, Jenner sneaks up the lee 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. Justin turns around and sees Jenner as he brings the sword up above his head with a snarl. Sullivan delivers the nearly-fatal blow to the nefarious rat, which strikes him in the back and kills him. Jenner soon falls off the cliff of the lee and dies.

Role in the series

Jenner was recruited by the Villain League to infiltrate the society of the rats, and then take the keyhole to this world. Spyro defeated him by going into his super mode, then obliterating the rat with an onslaught of fire.