Kariya Matou is the uncle of Shinji Matou, and the first scion of his family to be born with magical potential in several generations. Despite this, he grew disgusted with his family, particularly Zouken Matou, and cut all ties with them more than ten years prior to the 4th Holy Grail War. Disappointed with the lack of magical abilities in Shinji, Zouken resented Kariya for allowing the family's magical lineage to decline, especially since a Matō with magical powers was necessary to act as a Master during the Holy Grail Wars.
Kariya maintained contact with his childhood friend and love interest Aoi Zenjou, though he had willingly given up trying to pursue her affections after she married Tokiomi Tousaka. Aoi would later have two daughters, Rin and Sakura, who were both fond of Kariya.
(Source: Wikipedia)
