Onan, which is why wanking is called onanism. To me it’s an odd story because it seems more like a social construct than a divine command. So I wonder if it’s been heavily abridged and he died for some other reason that’s been left out and they just said God did it because they wanted to reinforce that construct. If God really had a habit of dropping bodies just for spilling their seed, well, let’s just say there’d be several thousand reasons why I wouldn’t be typing this right now.