Use 'in character' when someone's actions align with their established traits or history. My sister's excitement about the science fair was in character.
Pro Tip 2/3
Sudden Contrast
Highlight a surprise by contrasting actions that are not 'in character' for someone. He helped with the dishes? That's not in character for him.
Pro Tip 3/3
Analyzing Actions
Discuss or judge why someone did something by looking at whether it was 'in character'. Her donation was in character, given her past generosity.