If someone is curious, Delta (Δ) , Epsilon (Ε) and Gamma (Γ) are letters from the Greek...

I think all his clones were named in the greek alphabet & dat also explains how he manage to stay in the human world for quiet a long time

Yeah.. Gamma is the third letter of the greek alphabet so I suppose it was his third clone or it might actually be his second if he considers himself the alpha... Delta is the fourth letter and Epsilon is the fifth