Most ancient Greek proper names either names of gods, humans or animals as well as toponyms and hydronyms cannot be explained by Greek language, but by other Indo-European language which is the Pelasgian language being in the same time the substrate language of Greek. Robert Beekes, the author of the most recent Greek Etymological Dictionary shows that almost half of ancient Greek words are loanwords from the substrate language, but he does not say what language was it, although is obvious that it is a centum Indo-European language, quite different form Greek. I mention that the author of these lines identified hundreds of words in Greek which have close cognates in modern Romanian which is the real descendent of Pelasgian language. Briefly, the Greek substrate language was no other than Pelasgian, an older form of Illyro-Thraco-Dacian. In this article, the author shows that the personal name Achilles along with a few other names cannot be explained form Greek perspective, but from a Pelasgian one.