As for your question about Pantherghasts, Thorgrim, any sufficiently capable Celestial ritualist can summon and command Pantherghasts if he or she wished and had the materials to do so. Heck, I could do it if I so desired and had the necessary ritual supplies.
However, on a more notable note, whilst I might not know who exactly this lich is, I am certain that he is not who he claims to be; I was present when the Lich King McGregor was permanently destroyed just shy of four years ago.
Something here seems off.
~ Gandian Ravenscroft
The Magus of Tempered Rage