Answer:
MARK J. T. GRIFFIN wrote in his book Vangelis The Unknown Man:
Vangelis, which is pronounced Van (as in vantage), gel (GEHL with a hard "g" as in good), is (as in his) and is derived from his first name Evanghelos.
Incidentally, his surname is pronounced Papa (as in mama-papa), tha (a thick "th" as in Theodore), na (as in nasty), si (like see), ou (as in soon).