Lenny is one of a pack of saber-toothed cats, that was lead by Soto. Their pack initially was much larger but a tribe of humans had hunted down and killed many of the saber-tooths off, using their skin as coats. Soto felt that he was being wronged and made it his goal to steal the tribe's baby and eat it in vengeance. Lenny, among others in the pack, wanted very much to abandon their chase of the humans and their child, so as to follow the masses of migrating animals headed south. Soto's will was strong, however, and he viewed the taking of the baby as the perfect chance to teach the humans a lesson. The next morning, after expressing his beliefs, Soto arranged an attack on the human encampment.
Lenny, along with the others in the pack, attacked the human encampment, but was fended off by the humans' dogs, who fought alongside the humans against the pack, sending them off. One saber-toothed cat named Diego was expected to steal the baby from the humans, but he missed his chance when the baby's mother escaped with her child through a waterfall. Soto, angry at Diego's failure, ordered him to retrieve the baby and bring him to Half Peak, where the others would be waiting. Soto was later informed by Oscar that Diego would bring the baby back, along with a mammoth called Manfred, who had been watching over the baby, with the help of Sid.
Lenny met up with Diego, along with the others in his pack, at Half Peak, where Zeke reminisced on the joys of mammoth flesh, much to Lenny's displeasure. Lenny demanded that Zeke would stop reminding him of food, for Lenny was hungry, and about to hit Zeke when Soto intervened, telling them all to save their energy, as mammoths didn't go down easily. Soto was planning an ambush on Manfred, who must be caught by surprise, and so, he ordered the others to not attack, until they saw Manfred. Diego secretly turned on his pack after he had been shown real compassion and caring from Manfred and Sid that he had been leading into an ambush, and so Diego tempted Zeke to leap into action and to attack. The surprise being given away, the saber-tooths pursued Sid, as he slid down a snowy slope on a piece of bark. Soon after, Oscar and Lenny, who had been chasing Sid, were impeded by a large log, that Manfred threw at them with his trunk. Once Oscar and Lenny came to, they saw that Soto had been killed when he tried to attack Manfred and that Diego had intervened against Soto's attacks. Soto hit a wall of ice and a number of icicles came down on him, killing him. After seeing the death of their leader, Oscar and Lenny left the scene quickly.
- On the bonus material DVD in the deleted scene "Sabre Stake Out" , Lenny suggests that the pack head south for the "walking buffet".
- Lenny is not a saber-toothed cat like his compatriots, but rather a scimitar cat, closely related to saber-toothed cats. Most noted for his rotund build, Lenny is considerably thicker than the others in his pack, and had a matching appetite. Lenny had hazel eyes and shorter fangs than his fellows, as well as a light tan pelt.
- There is a mistake where Soto tells him the only way to take down a mammoth. When he says "I'll go for the throat," Oscar is on the left, and Zeke is on the right. When the camera goes to them again, they switch sides!