Mark (In Which Dell Finds His Fight)

Mark is the brother of Jeffrey.

History
When Mark's brother, Jeffrey, and sister-in-law, Kathleen, found out they had a very low chance of conceiving a baby together due to Jeffrey's low sperm count, Jeffrey, desperate to give his wife the baby she wanted, approached Mark to be the sperm donor. He happily gave his sample and it was good, so they went to inseminate, but Jeffrey and Kathleen both stopped it at the last minute.

Familial
He agreed to donate sperm so his brother and sister-in-law could have a baby. However, they ultimately didn't go through with it because he's kind of a jerk.