Back when I was in college another bicyclist ran into me from the side and it put a bad bend into the rear rim. The rim was bent about 20 degrees out of true and was way past anything that could be fixed by regular truing via spoke tension. I disassembled it completely and then took the bare rim to the top of a stairway. Positioning the bent portion over the edge of the top step, I had a friend stand on top of the part that was fairly flat while I put some weight on the bent part. Once I thought it was close enough to all being in the same plane I laced it up using the other wheel as a guide and trued it in the bike frame with my spoke wrench. That was the first wheel that I ever built and it lasted for several more years and thousands of miles before I sold the bike.