If this topic has been mentioned before, I haven't seen it. :P
The character doesn't need to be someone you use on every play through. Maybe they are a bad/underused unit? Maybe they are disliked across the community? Just... you use them from time to time even when the world is against you. (Maybe not that extreme)
If you have more than one, feel free to put them in, too! Everyone deserves a time to shine!
Also, be sure to put which fire emblem game the specific unit/character is in.
Mine are:
Macellan from FE 11. His armor is a different color than everyone Else's and he's just so serious about his duty. Plus he makes a good Hunter for me when reclassed.
Marisa from FE 8. She's hot. She's not very sociable, like me! And I just really like her sprite's design.