Adam Clarke on Acts 6:5

Stephen, a man full of faith and of the Holy Ghost - A person every way properly fitted for his work; and thus qualified to be the first martyr of the Christian Church.

Nicolas, a proselyte of Antioch - A heathen Greek, who had not only believed in the God of Israel, but had also received circumcision, and consequently was a proselyte of the covenant; for, had he been only a proselyte of the gate, the Jews could not have associated with him. On the word proselyte, see the note on Exo 12:43. As this is the only proselyte mentioned here, we may presume that all the rest were native Jews. From this Nicolas, it is supposed that the sect called Nicolaitans, mentioned Rev 2:6, Rev 2:15, derived their origin. Dr. Lightfoot doubts this, and rather inclines to derive the name "from ניכולא nicola, let us eat together; those brutes encouraging each other to eat meats offered to idols, like those in Isa 22:13, who said, Let us eat flesh and drink wine, etc." Both Irenaeus and Epiphanius derive this sect from Nicolas the deacon. Clemens Alexandrinus gives this Nicolas a good character, even while he allows that the sect who taught the community of wives pretended to derive their origin from him. See on Rev 2:6 (note).