There was a historian called Josephus who documented various events around that time, and he mentions Jesus. That in itself isn't enough, but if you take it along with the Bible, it seems enough to suggest that there was a man named Jesus who lived, and was politically active. He also mentions John the Baptist.
If you take the Bible to be at least partially accurate, the things most likely to be true are the ones without the magical elements about them: that he lived, taught, and was arrested and sentenced to death.