He looks the same as Squidward and wears a brown shirt. And he wears a tie and glasses.
He was mentioned in "Krab Borg" when SpongeBob told Mr. Krabs that Squidward's father never loved him. Squidward then claimed that his father loved him very much. The use of past tense has led to fan speculation that Mr. Tentacles is deceased, although past tense was likely used to indicate that Squidward was loved in the past as a child. However, he made a physical appearance in the book Hooray for Dads!, indicating he is alive. Mr. Tentacles was shown to have a similar personality to his son.
Besides Mr. Krabs, he is the only dad in the book Hooray for Dads! who did not have a mustache.