(interrogative) Who ever: an emphatic form of who.
Whoever thought up that stupid idea?
(fused relative) Any person or persons that.
Whoever breaks the law will be punished.
(fused relative) The person that (no matter who).
I don't know what it is. Ask whoever put it there.
Regardless of the person or persons that.
Whoever stole the painting, the police will catch the thief in no time.
Any person or persons.
I don't care who gets it; give it to whoever.
Misspelling of who ever other than in interrogative use.
*He is the tallest man whoever lived. (incorrect usage)