Teron Gorefiend was a death knight... yes the Horde had death knights before the Scourge... play warcraft 2...
And no there is not a lot of notable mortal warlocks just because of how they are looked down upon by most and so usually practice their art in secret...
---------- Post added 2010-09-02 at 06:49 PM ----------
If you didn't figure it out when locks took the demon hunter main ability then let me spell it out for you... warlocks are the playable version of demon hunters... there will never be a demon hunter class... all demon hunters were basically warlock/rogue hybrids anyway...