In chapter two of Steinbeck's novella Of Mice and Men, both George and Lennie, who are traveling together as migrant farm workers, reveal their last names in the conversation with the boss of the ranch where they have come to "buck barley." George is George Milton and Lennie is Lennie Small. Lennie's last name is ironic because Steinbeck characterizes Lennie as a physically imposing man, "a huge man, shapeless of face, with large, pale eyes, and wide, sloping shoulders." In the discussion with the boss, George describes Lennie as "strong as a bull." Later in the same chapter the laborer Carlson makes a joke of Lennie's name when the men are introduced:
“Glad ta meet ya,” the big man said. “My name’s Carlson.”
“I’m George Milton. This here’s Lennie Small.”
“Glad ta meet ya,” Carlson said again. “He ain’t very small.” He chuckled softly at his joke. “Ain’t small at all,” he repeated.
The small part of Lennie appears to be his level of intelligence. Because Lennie has trouble understanding his environment and his own strength, throughout the novel he does things that most adult men would not do, such as grabbing a girl's dress, killing small animals such as mice and puppies, and finally accidentally breaking a woman's neck.
Ironically, Lennie's last name is Small.
Remember that Lennie's superhuman physical strength and dwarfed mind lead to his downfall.