I would need more context but I think this is a slang combination of ``What a``... like ´´whatta great person!!`` In more formal speech it should be ´´what a great person!``

that is ´´What a man!``` it´s an expression meaning this man is great, a good man. When someone uses ´´what a + noun``, it a way to call out how great it is. ``Whatta catch!`` ``Whatta man!`` ``What a great lunch!`` etc.