6.

Er was wicked in the sight of the Lord (so the Lord slew him)

This is the first of God's named murder victims.

We know his name (Er), his father's name (Judah), and his wife's name (Tamar).

Judah saw there a daughter of a certain Canaanite, whose name was Shuah; and he took her, and went in unto her. And she conceived, and bare a son; and he called his name Er. ... And Judah took a wife for Er his firstborn, whose name was Tamar. Genesis 38:2-6

And we know that "he was wicked in the sight of the Lord; and the Lord slew him." But that's it.

Er, Judah's firstborn, was wicked in the sight of the LORD; and the LORD slew him. 38:7

God killed Er for doing something, but the Bible doesn't say what it was.

So what did Er do?

Did he get drunk and lie around naked in his tent and then curse his unborn grandson (and all of his descendants) with slavery because his son saw him drunk and naked? No that was Noah, "a preacher of righteousness." (Genesis 9:20-25, 2 Peter 2:5)

Did he abandon his first son to die in the desert and then show his willingness to murder his second son for God as a human sacrifice? No, that was Abraham, "the Friend of God." (Genesis 21:10-14, 22:2-12, James 2:23)

Did he offer his two virgin daughters to a sex-crazed mob of angel rapers and then get drunk and impregnate them? No that was Lot, a just and righteous man. (Genesis 19:8, 30-38, 2 Peter 2:7-8)

So what was it that pissed off God so much that he just had to kill him?

You'd think if it was important enough to kill him, it would be important enough to tell us why.