Widmore was an Other!

Widmore served as an Other on the island under the command of Richard Alpert in 1954. He was captured by Locke, Juliet, and Sawyer but escaped and returned to the Others' camp. He unknowingly leads Locke's group to this camp. As Locke enters the camp, Widmore aggressively points a gun to Locke's head ordering him to stand down. After Locke wins Richard's trust, Richard identifies Widmore by asking him to lower his weapon. Locke also recognizes the name. - Lostpedia

Thanks to Lostedia and The ODI for the images.