split personality

Translations
раздвоение личности
He seems to have a split personality, being kind one moment and harsh the next.
Кажется, у него раздвоение личности: он добрый в один момент и строгий в следующий.
Definitions
A psychological condition in which a person exhibits two or more distinct identities or personality states, each with its own pattern of perceiving and interacting with the world, often associated with dissociative identity disorder.
Words
split

adjective
раздвоенная
personality

noun
личность