Onan

Onan was the second son of Judah. Required to impregnate his deceased brother's wife so his brother's line would not die out, Onan instead enjoyed sexual union with her but chose to make sure impregnation would not take place by spilling his seed upon the ground. (Genesis 38:9) "And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother."

Because of his actions, he was slain by God. (Genesis 38:10-11). The sin of onanism is named for him.