Originally Posted by OutRiddled
I wanted to see why he was nicknamed "Harvey Two-Face".
Someone who is two-faces presents themselves one way while acting in a different way. Harvey presented himself as being an honest man, yet he investigated cops behind their back - that's what internal affairs does. Clearly this was not lost on the cops themselves:
GORDON: "If I didn't work with cops you investigated while you were making your name at IA, I'd be working alone."
Hence the name Harvey Two-Face.