An alter ego (Latin, "the other I") is a second self, which is believed to be distinct from a person's normal or original personality. A person who has an alter ego is said to lead a double life. The term appeared in common usage in the early 19th century when dissociative identity disorder was first described by psychologists. Cicero was the first to coin the term as part of his philosophical construct in 1st century Rome, but he described it as "a second self, a trusted friend".