Capricious adjective \kə-ˈpri-shəs, –ˈprē-\
a: changing often and quickly; especially : often changing suddenly in mood or behavior
We survived off him as if he were a capricious and dangerous line of work. I suppose we stopped thinking of him as a human being, certainly as a father.
The Shawl paragraph 11
He was an unpredictable dangerous kind of person who was best avoided.