Pencilvester is a false character, portrayed by the Alien Parasites in the episode Total Rickall.
History
He is an anthropomorphic pencil who is apparently great lifelong friends with Rick Sanchez and Morty Smith. Rick loves him so much, that he was hesitant to kill him, even when he knew he was an Alien Parasite and had Morty do it for him while looking away. Morty also loves him so much, that he refused to kill Rick in front of him, although when Rick had told Morty to kill Pencilvester the latter didn't hesitate to shoot him through the chest.