In In Dubious Battle, Steinbeck's all about showing us the difficulties that arise when an individual becomes part of something "larger than himself." Just take a look at what happens to Jim. He comes to Party headquarters as a shell of a person destroyed by the injustice of an impersonal and uncaring social system. And without a will to live, there's not much to define his personality. The one defining thing he has is his desire to be somebody—anybody.
Jim finds the communal spirit of the Communist Party refreshing. Party memberships wakes him up and gives him a sense of purpose again. But in taking on the group identity, Jim has no need to rebuild his own personality after a lifetime of defeat. Instead, he becomes part of "group-man," a term that Doc uses to describe people who have given up their personal identities in the service of a larger "organism."
Although Jim stands apart from the group because he can lead, he's still little more than fodder for the cause. He quickly surpasses Mac in his willingness to put his humanity aside when the need arises—something that totally freaks out his mentor. In the end, Jim suffers a fate symbolic of his growing dehumanization and his loss of personal identity in service to a larger goal: he becomes literally faceless.
Questions About Identity
Why does Jim look "drunk" or "asleep" when he first meets Henry Nilson?
What is Mac's philosophy about personal preferences, especially when on assignment for the Party?
In what ways does Doc Burton's description of group-man match that of a mob? In what ways does it differ?
Why does Mac say that he's become afraid of Jim?
Chew on This
Jim's destruction, though completely awful, is probably necessary because of his hideous transformation over the course of this novel.
Mac's ability to "shape shift" when he gets involved with new people shows that he actually has a high degree of empathy with others.