ED- is a possible companion in Fallout: New Vegas. Unlike some companions you don't have to complete a quest to access him. You must repair him. He is on the desk of Johnson Nash's shop, to repair him you need either 65 Repair, or 1 scrap electronic, 2 scrap metal, and 3 Fission Batteries. After repairing him you can instate companion protocol and have him as a companion. He is almost certainly the first possible companion.