Lenny (a.k.a. the "Dumb Gremlin" and "The Goofy Gremlin") is a tall, idiotic, light skinned, bucktoothed gremlin and as a mogwai, his fur was light-brown and white and he had has black stripes on his face. He is generally the least aggressive or dangerous gremlin besides the Brain Gremlin who was not directly dangerous towards humans but more evil than Lenny. He is also the only one not to have razor sharp fangs. Instead he has human like teeth with big buckteeth that stick out in front. (However, he does everything that George and Mohawk command him to do).

He is George's partner in crime as he is always following him, George often using him for heavy lifting. Lenny often accidentally hit him with everything he carried, greatly annoying George. He is the second fully developed mogwai to be seen and he along with Mohawk and George approaches Gizmo, from whom they spawned. George orders him to tear a nearby went grille open and he does, managing to hit George with the grille as he pulls it out. The three of them then shoves Gizmo inside the ventilation shaft and Lenny then puts the grille back into place and laughs before heading off with the other two mogwai. They then hitches a ride with the Clamp Center Janitor to the lobby where they eat at a yoghurt shop before heading off and going into cocoons.

He is first seen in his gremlin form, wearing a chef's hat and apron, when he along with George and Daffy crashes the Microwave With Marge show being filmed in the Clamp Center building and it ends with him and his two companion gremlins getting wet and spawning new gremlins. Later he is seen along with George in a toy store and manages to knock over George's Lego Gremlin and isolator seen in the control room, watching the monster movie 'The Beast From 20,000 Fathoms' and after that, he plays around with the ventilation system. Later he is seen together with George, Daffy and the Brain Gremlin and the other Gremlins as they perform the song "New York, New York" with Brain as the lead singer. He is killed along with the remaining gremlins when the Electric Gremlin is unleashed at them after they are sprayed with water from a hose. He dies together with his partner in crime George.

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