Mr. Crocker's grandfather has appeared in a couple of episodes, but has had no major roles in the series.
He looks almost exactly like Mr. Crocker, but he is bald, has hairy white eyebrows and a long white beard; he also wears bottlecap glasses.
He was first seen in the episode "Bad Heir Day" in the Crocker's House on a picture hanging on the wall, opposite of a picture of Crocker's mother.
In "Old Man And The C-", Mr. Turner had to go back to the fifth grade since he dropped out when he was a kid, he wrote an essay on grandfather clocks for class. In his essay, Mr. Turner pointed out that grandfather clocks are not made with real grandfathers, causing Mr. Crocker to panic and release his own grandfather from a clock he built.
Due to the fact that Crocker's mother is elderly herself, Grandpa Crocker must be extremely old.