While Of Mice and Men occurs in a very specific time and place, each of the characters can be thought of as symbolizing broader populations. Though the book is not an allegory, and each character can stand alone as simply a character, there’s still something to be gained by looking at each character as representative of their larger group. Here we go.
Lennie is symbolic of the archetypal "wise fool," who is mentally inferior but able to reveal the best and the worst of others. Lennie’s foolishness often allows him to speak honestly where others won’t, and he sometimes taps into things that "normal" people can’t (like the fact that the ranch isn’t a good place for him and George to be hanging out). Lennie is also symbolic of people who are mistreated and discriminated against because of their mental handicaps.
Curley’s wife is symbolic of Eve – the female character who, in the Biblical story, brings sin and death to the world. She is also symbolic of women everywhere who are repressed by male-centered societies.
Curley is symbolic of "small" people who may feel inferior and overcompensate by inflating or flaunting their power and status.
Crooks is symbolic of people who are discriminated against because of their race.
Candy is symbolic of people who are undervalued and discriminated against because of their age.
Carlson is symbolic of people who are oblivious to the feelings of others, and who can only be concerned about something if it affects them personally.
Slim is symbolic of the archetype of the hero, king, or leader. He represents those few who, in their wisdom and strength, seem larger than life.
George is symbolic of "the everyman" – the type of normal, average person who is found everywhere and whose feelings and actions are neither exceptional nor terrible. He is the character with whom most readers will identify, as he symbolizes the difficulty of trudging through the everyday world (and extraordinary situations) when you’re just an ordinary guy.