Sir Philip Jermyn was the son of Wade Jermyn and the great-great-grandfather of Arthur Jermyn. Described as a "highly peculiar" person, he was the first of his father's descendents to exhibit the simian characteristics that originated from the union between Wade Jermyn and a female member of a race of African white apes. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")
Despite a strong physical resemblance to his father, his appearance and conduct were so coarse that he was universally shunned. He did not inherit the madness which was feared by some, but he was densely stupid and given to brief periods of uncontrollable violence. He had a small frame but was very powerful and had incredible agility. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")
Twelve years after gaining his hereditary title Sir Philip married the daughter of his gamekeeper, but before his son Robert was born he joined the Navy as a common sailor. After the end of the Revolutionary War he became a sailor on a merchant ship in the African trade, having a reputation for feats of strength and climbing. Philip eventually disappeared one night as his ship lay off the Congo coast. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")