斉木 熊五郎

He 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. 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.

(Source: Saiki Kusuo no Psi-nan Wikia)