Gyles Blackthorne was the second-born son of Jacques Blackthorne and his wife Hadriana Hassarath. His elder brother was Arthur Blackthorne, the Third Lord of House Blackthorne; his nephew through Arthur was Malcolm, the Fourth Lord; and his own son, Lucas, was the Fifth. Gyles is notable for being the first elected Hand in the history of the family, assuming the position after his brother died in 382AE. From infancy, Gyles had always been a pragmatic and logical individual, greatly enamored with arithmetic and literature. His gaunt frame made him a poor warrior, and he would frequently shy away from the practice field in order to spend time in the libraries and archives in Griffin's Peak. As his nephew was only 14 when he ascended to power, it was judged that Gyles' academic ability would be put to good use in an advisary capacity to the young lord. Gyles took the offered position a step further and became both a regent and mentor to his nephew. By the time Gyles had passed away from consumption in the winter of 399AE, he had passed all he'd learned to Malcolm, who used the knowledge well as the Good Griffin.
Gyles was in a loveless marriage with Hieronymus Rookwood's only daughter Anja. It was said he was intimidated by the girl and spent most of the time that he should have spent sharing her bed in the library instead. Nonetheless, they managed to have a child; Anja died delivering their son Lucas, who would grow to become the infamous Usuper Griffin.