Idiosyncratic – of, characterized by, or resulting from idiosyncrasy
Idiosyncrasy – the temperament or mental constitution peculiar to a person or group; any personal peculiarity, mannerism, etc
“But politics suited [Theodore Roosevelt’s] temperament and ambition. It would fuel his abundant vitality and need to be on the go and make things happen. For a gentleman, his career choice was not idiosyncratic.”
Lion in the White House, Aida d. Donald