Who were the Nicolaitans?
The work "Nicolaitan" is only mentioned in Revelation 2:6 and 2:15. It comes from the Greek word nikolaites which literally means "a follower of Nicolaus."
Nicholas was a name used by some. For instance, one of the early deacons mentioned in Acts 6:5 was called Nicholas ("nicolaus" in the Greek). Whether this is the same Nicholas mentioned in Revelation or that there was another is pure speculation. The name Nicholas means "conqueror of the people" and there is a subtle play on words being done in Revelation because the followers are Nicholas are being compared to the followers of Balaam. "Balaam" in Hebrew means "destroyer of the people."
Revelation 2:6 tells us that Christians in Ephesus stood against the followers of Nicolas. Revelation 2:14-15 tells us what the group taught. "But I have a few things against you, because you have there those who hold the doctrine of Balaam, who taught Balak to put a stumbling block before the children of Israel, to eat things sacrificed to idols, and to commit sexual immorality. Thus you also have those who hold the doctrine of the Nicolaitans, which thing I hate." While the teachings of Balaam destroyed the people of Israel, the teachings of Nicholas has destroyed Christians. The implication is that it was based on similar teachings - idolatry and sexual immorality. If this is true, then the church in Thyratira was struggling with the same issues. "Nevertheless I have a few things against you, because you allow that woman Jezebel, who calls herself a prophetess, to teach and seduce My servants to commit sexual immorality and eat things sacrificed to idols" (Revelation 2:20).
Followers of Balaam, who were compared to the followers of Nicholas, are mentioned elsewhere in the New Testament (II Peter 2:15 and Jude 11).
Irenaeus, who lived about 180 AD, had this to say about the group. "The Nicolaitans are the followers of that Nicholas who was one of the seven first ordained to the diaconatee by the apostles. the Nicolaitans lead lives of unrestrained indulgence. The character of these persons is very plainly pointed out in the Apocalypse of John. It shows that they teach that it is a matter of indifference to practice adultery and to eat things sacrificed to idols."
Clement of Alexander, who lived about 195 AD, wrote, "Those who say that they follow Nicholas quote the adage of that man -- "The flesh must be abused" -- which they pervert. but that worthy man [Nicholas] actually meant that it was necessary to curtail pleasures and lusts."
Tertullian, who wrote about 207 AD, stated, "I do not aim at destroying the happiness of sanctity, as do certain Nicolaitans in their maintenance of lust and luxury."
Whether Nicholas founded the group or whether later men twisted Nicholas' teachings to create their own beliefs, it is a group that sought after sensuality and thereby left the truth of the Bible. You will find some who build complex arguments that the Nicolaitans came up with the clergy / laity system. It is all built around the fact that “people” is found in the name Nicolaitans and “laity” is also derived from the word for “people.” Since the clergy system was not documented to have developed until the third or fourth century, yet John writes about the Nicolaitans in the first century, it is clear that the two ideas have nothing to do with each other, other than that they both involved people.