The Watcher is a being that lives in Space and "watches" everything. He is a neutral being that will not help anyone.
The Watcher appeared in Marvel's Avengers Assemble as a cameo, where he and the Hulk were watching a baseball game. Watcher made a full appearance in Hulk and the Agents of S.M.A.S.H., living on the blue side of the moon, an area where there is oxygen. He watched the Agents of S.M.A.S.H. take on their Jump Jet.