Genesis

He first showed up in Genesis chapter 14.  There had been a war between the king of Sodom (where Lot had chosen to live) and his alliance, and a stronger four king alliance.  The stronger alliance, of course, won, and carried the people and goods of Sodom away.  Abraham (then called Abram), would not have been concerned except for the fact that they had taken captive his nephew, Lot, and his family.  He organized the men of his own household along with some men from Aner, Eshcol, and Mamre.  Long story short, they conquered the stronger alliance of kings and got all the people and goods back.