What religious beliefs did the Galatians hold when Paul first preached the gospel to them? When Paul originally proclaimed the Gospel to the Galatians, were they at that time pagan, Jewish, or something else. Did they ever hear of Christ Jesus before Paul?
For reference:

You know that because of physical infirmity I preached the gospel to you at the first. And my trial which was in my flesh you did not despise or reject, but you received me as an angel of God, even as Christ Jesus.
Galatians 4:13-14
The Wikipedia article on Galatia states that the Galatians were Celts who invaded the area about 275 BCE, and who were reported to be in the area until about 475 CE, or so. It is likely that the Celts would have been considered "pagans" by the local population as they seem to have taken some time to adopt local ways. However, the Galatians do not seem to have comprised the entire population of the area, but rather only a ruling class. And the reports of Paul's activity refer to "in Galatia", which seems to be the region, and in the absence of other evidence, does not seem to be any to prove that the Galatians were the primary group among which Paul was evangelizing. 

Acts 18:23 relates that after spending time in Caesarea and Antioch, Paul traveled through Galatia "strengthening the disciples there" (RSV). The fact that Paul "strengthened", rather than "made" these disciples suggests that some had already been evangelized, but there is not enough information to determine whether the earlier evangelization was by Paul himself, or by someone else. We also don't know whether among those with whom Paul interacted, that there might not have been some who had heard of Jesus Christ, but were not yet believers. However, it is likely that Paul also interacted with non-Christians, and non-Jews in Galatia, so some of the people he evangelized may have not already have heard of Jesus, or if they had heard of him, may not have believed he was the Christ.

Galatians 4:13-14, seems to suggest that when Paul originally traveled through Galatia, he suffered some sort of unspecified infirmity; and seems to be an exhortation to some of the Galatians to maintain steadfast in faith.  We're not given enough information to determine what that infirmity might have been.