Um Tentacles is a fictional character who appears in the episode "Scavenger Pants."
"Um" looks exactly like Squidward, except that he has a big, black mustache, which was drawn on by Squidward.
Role in episode
After many failed attempts to get rid of SpongeBob and Patrick in his scavenger hunt, Squidward tells them to find his make-believe long lost brother in an attempt to get rid of them for good. When they ask him what his name was, Squidward tries hard to think of a name and says, "Um...," causing them to think that was his name.
It takes 6 months for them to find him (they even think Squidward himself was "Um," assuming he shaved off his mustache). They then go to Mrs. Tentacles' house and find out that "Um" was a fake. They end up thinking Squidward feels lonely without a brother and have Mrs. Tentacles adopt them, becoming Squidward's new adopted brothers.