He’s a changed person.
He’s a strange character.
I think 変わった, when describing a person, almost exclusively means “strange” – like 変。
Agreed with @ericaw .
“He’s a changed person” should be 彼は人が変わった (his personality/attitude has changed).
変 in 彼は変わった人だ means “strange” or “to have an unusual (sometimes unique) taste/tendency”. 変態 (へんたい), for example, is derived from the same meaning.