Saiki Kumagoro

 Kumagoro Saiki (斉木 熊五郎, さいき くまごろう lit. Saiki Kumagoro) is the husband of Saiki Kumi and father of Kurumi, the father-in-law of Saiki Kuniharu and grandfather of Saiki Kusuo and Saiki Kusuke.

Background
Kumagoro is a grumpy old man who hates Kusuo's father and loves his daughter. He is actually a tsundere who truly wants to dote on his grandchildren. He is surprisingly getting along with Riki.

Trivia

 * His name,, is a pun on the word Psychic (サイキック Saikikku).