how is the character lennie presented in the novella of mice and men

When we first meet Lennie, he is travelling with George to their ranch job. Lennie is easily characterized as slow or mentally challenged. Lennie can't remember where they are going and George needs to remind him, "I gotta tell you again...Jesus Christ you’re a crazy bastard!" Lennie does childish things like hold onto a mouse. There is still innocence about him even though he is in the body of a strong man.