Theon is a bastard. His biological father is Euron Greyjoy, because Balon has a small penis. Throughout A Song Of Ice And Fire that cuckoldry is a common occurrence.Theon doesn’t resemble Balon, and his other older brothers. Here are a few similarities between Euron and Theon. Theon is described being handsome, and has swag like Euron. Not to mention Theon has a dark sense of humor like Euron. Things to consider: 1). Euron would have no problem with sleeping with Balon’s wife.
2). Balon abandons Theon because he knows deep down Theon isn’t his son.
3). Theon had a big penis, and sleeps around.
4). Balon would be have a hard time getting his wife pregnant. He was already old.