Onan was the second son of Judah. He helped coin the term “onanism,” known around these parts as “pulling out.” It got him killed.
“According to the text, after God had killed Onan’s older brother Er, Judah asked Onan to have sex with Tamar, Er’s widow, so that the offspring could be declared Er’s heir,” explains the Wikipedia entry. “The narrative implies that Onan didn’t object to the sex itself, but performed coitus interruptus, spilling his seed upon the ground, so that there wouldn’t be any offspring which he could claim as his own. The passage then goes on to state that, for this act, a displeased God killed him. The deaths of Onan and Er are among the few deaths caused by God which the Torah doesn’t describe as being caused via an intermediary, such as plague, or the Angel of Death.”