Large and friendly with a mental disability

"I was only foolin', George. I don't want no ketchup. I wouldn't eat no ketchup if it was right here beside me."

"If it was here, you could have some."

"But I wouldn't eat none, George. I'd leave it all for you. You could cover your beans with it and I wouldn't touch none of it."

These quotes show that Lennie was harmless and he didn't mean to do anything bad. He was very friendly and didn't mean to harm anyone.

Of Mice and Men (1939) Full Movie
Lennie was just trying to do things that just made him happy. No one realized that except for George. Lennie just liked soft things and he didn't ever want to get into trouble. He wanted to have a farm with George and just live happily together with soft animals. All the way until the end he didn't mean to hurt anyone.