Several New Testament writers use the term "God-fearers." Does this refer to an actual group or is it another name for Paul's opponents?
To answer that completely, it might be helpful to consider three of the various religious groups associated with Judaism and Christianity in the first century. On one end of the spectrum would be traditional Jews. On the other end would be Gentiles, who might be involved in all sorts of religious experiences and who might have followed many pagan gods. In the middle, were the God-fearers.
We know from Acts that many Jews converted immediately after hearing the disciples speaking in their native tongues at Pentecost. At that time, those converts were not yet identified as Christians; they would have thought themselves Jews who followed Jesus' teachings. Later on, they would become known as Jewish Christians. This group would have included Jesus' twelve disciples, his other followers, and all those newly converted Jews.
Within a few years, Paul and the other disciples would start converting large numbers of Gentiles. This group would initially be referred to as Hellenized Christians or Gentile Christians. Later on, they and the Jewish Christians would simply be known as Christians.
That brings us to the third group, known as God-fearers. Scholars believe this group existed long before Christianity came on the scene. These Gentiles were sympathetic to Judaism and interested in at least some of its teachings. They might have attended the local synagogues and adhered to some of the Jewish dietary restrictions. Some of them might have observed the Sabbath as a day of rest or even have studied the Torah. However, most scholars think they would have drawn the line at circumcision. Obviously, there would have been a lot of latitude among the God-fearers as to how strictly they embraced and practiced the teachings of Judaism.
Scholars also feel that the influence of the God-fearers extended well beyond the doors of the synagogue. Because God-fearers were not Jews, they were well integrated into all levels of Greek society. Some of them were quite prominent.
There is an interesting situation described in Acts. Paul had been preaching in Pisidian Antioch. Since the Jews were not listening to the word of God, he turned to the Gentiles. The Gentiles were thrilled, but the Jews weren't. They "incited the God-fearing women of high standing and the leading men of the city. They stirred up persecution against Paul and Barnabas and expelled them from the region." (See Acts 13:49ff) Clearly god-fearers existed and had high standing and clout. They could get things done – like getting rid of Paul and Barnabas. In this case, the God-fearers were women who were very supportive of the Jews.
It is likely that the God-fearers facilitated the integration of Jews within the Greek community. Some of them even acted as benefactors for the Jewish community. Inscriptions indicate several prominent citizens built synagogues in various communities and contributed to Jewish charities. Josephus (a first-century historian) wrote that almost all of the women in Damascus were devoted to Judaism. Documents attest that many relatives and wives of royalty were also interested in Judaism.
When Paul came on the scene, he always started preaching in the synagogue of the town he visited. There he found eager converts among the God-fearers. They heard from Paul's preaching that they were accepted by God. They worshiped God and followed his teachings and led righteous lives – Paul told them that was enough to be fully accepted into the Christian community. In fact, the whole encounter with Cornelius in Acts 10 demonstrated that the Holy Spirit was with them fully.
As Christianity progressed and many more God-fearers converted, the Jews had a vested interest in fighting for the hearts and minds of the God-fearers. In some cases, the Jews' very existence in their own communities might have depended on it. Yet, the fact that Christianity continued to grow and prosper suggests it was a fight they were losing.