“Now the LORD appeared to him by the oaks of Mamre, while he was sitting at the tent door in the heat of the day.” Gen. 18:1

Mamre is the Amorite who Abraham is friends with, who also went into battle with him against the four kings. (Gen. 14:13) Apparently not all Amorites were wicked, though God was storing up judgment for them patiently, to come 400 years from now when the Israelites leave Egypt and begin to take the Promised Land by force. (Gen. 15:16)