1
general::
Consistent with someone's general personality or behavior. For example, Her failure to answer the invitation was completely in character. This usage dates from the mid-1700s, as does the antonym, out of character, as in It was out of character for him to refuse the assignment.
American Heritage Idioms
2
general::
Phrase(s): in character
Fig. typical of someone’s behavior. • For Tom to shout that way wasn’t at all in character. He’s usually quite pleasant. • It was quite in character for Sally to walk away angry.
McGrawhill's American Idioms And Phrasal Verbs