Crooks and Candy share a powerlessness and an isolation in Of Mice and Men.
Crooks has no friends and lives alone in the stables. He is the only non-white character and for this reason he is isolated. Additionally, Crooks has a crooked back and this physical problem renders him incapable of many kinds of work.
Candy also has a phsycial handicap. He is missing one hand. Physically incapable of doing the same work as the field bucks, Candy and Crooks are both relegated to minor tasks around the bunk house and the stables.
Like Crooks, Candy has no friends. This is especially true after Candy's dog is killed. Friendless and weak, these two characters occupy the lower end of the social ladder on the ranch along with Lennie and Curley's wife.
A final similarity shared between Crooks and Candy is their response to the dream that George and Lennie present. Each man doubts that the dream is really possible to achieve then becomes quickly convinced of its possibility, growing excited to join the group.