Zeoticus Gremory

Lord Gremory is the current head of the Gremory Clan of Devils. He is the father of Rias Gremory and Sirzechs Lucifer and grandfather of Millicas Gremory.

A middle-aged looking man with crimson red hair.

Coming from the Gremory Clan that has extra-ordinary affection, Lord Gremory has demonstrated a very kind disposition.

Little is known of Lord Gremory's past, except that he married Venelana Bael and eventually fathered two children: Sirzechs and Rias. When Sirzechs became the Satan, "Lucifer" and lost his right to become the Head of the Gremory Clan, Lord Gremory made an arrangement with the Phoenix Clan for his daughter to marry Riser Phoenix at some point before the series.

When the girls of the Occult Research Club are ordered to begin living with Issei, Rias asks her father to renovate Issei's house into a mansion. Though the house he designs has three floors, two basements, an underground pool and a massive kitchen, the mansion he originally had in mind was to be much bigger and staffed with many maids.

Lord Gremory seems to get along well with Issei's parents and even seems to take for granted that Issei will end up with Rias anyway, once calling Issei "Son."

(Source: High School DxD Wikia)