Matou Zouken

A freaky old bug man. The end.
The scenario director is quite fond of him, and would get carried away typing every time he appeared.
He belongs in a harlequin novel, don’t you think?

Fate/side material: Fate Encyclopedia

As far as the Matou family’s sacrifices in the Fourth Holy Grail War go, for the small price of a ruined home defense barrier and a grievous injury to Byakuya’s wrist, they were able to get their hands on fragments of the Holy Grail. Too cheap, too cheap! Grandfather is laughing.
Though Zouken allowed Kariya to participate in the Grail War, he mostly did it just to punish him—if Kariya had actually won, he probably wouldn’t even know how to react.
Originally, Zouken had been content to turn a blind eye to Kariya’s transgressions as long as he was living the wretched, fearful life of a runaway, but his extremely un-Matou-like willingness to heroically sacrifice himself bought him the old man’s ire. Probably, it was the warped pride of a living, rotten corpse at work. Like, “When did my own flesh and blood get so damn impudent!?” or something to that effect.
By the way, Zouken thought that Kariya had died when all the crest worms were killed by Berserker’s rampage. The reason that Kariya, finally free, was able to return to the Matou mansion and reach Sakura’s side without any issues, was because Zouken had rushed off to the scene of the fire to see if he could find anything worth salvaging. In fact, they must have literally just missed each other. It seems Kariya has a talent for seizing odd strokes of good luck at the height of misfortune.

Fate/Zero material: Fate/Zero Encylopedia