He looks identical to his son Squidward, as he wears a brown shirt, the only differences with him and Squidward is that his shirt is a lighter shade of brown, and he wears a red tie and glasses.
He is mentioned in "Krab Borg" when SpongeBob tells Mr. Krabs that Squidward's father never loved him. Squidward then claims 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 makes a physical appearance in the book Hooray for Dads!, indicating he is alive. Mr. Tentacles is 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.
He acts very similar to Squidward Tentacles, indicating it might run in the Tentacles family.