We don't necessarily have to just believe in what has been recorded. Confidence in the Dhamma helps to bring confidence in the Buddha. If we have confidence in the Dhamma and then reflect on how the Dhamma came to be, on the dependent arising nature of the Dhamma, we also get insight into the Sangha and the Buddha. As we use the Buddha's teachings and understand how they work, gaining experiential confidence in them, our confidence in the original teacher and where the teachings originated arises. Actually, if we consider the depth and the wisdom of the Dhamma, it's very inspiring to imagine someone who could understand this without receiving any teachings. It's hard enough for us, when we have a teaching and scriptures to guide us.
Because, sometimes, I am in the position of having to figure out how to do things without having anyone to guide me - how to put retreats together, for example - I sometimes understand the difficulty in being the first. Yet, I have the Dhamma to guide me. I have these wonderful Four Noble Truths to help me, to apply to my life. That helps give me strength and courage in these instances.
If we develop a strong confidence in the Dhamma, then, to me, confidence in the Buddha automatically follows. We can consider what qualities would be necessary for a person to uncover such deep truth and to then put it in a form that is able to be taught to anybody, regardless of race, sex or age, containing different levels of the Dhamma, and given for people who have different goals, for those who are in the world and for those who want to reach the highest level of their potential.
So one does not necessarily have to know the Buddha as a person and have met him, or even believe in the biography of the Buddha, but when one takes his Dhamma, tests it, and sees it working, one naturally comes to a confidence in anyone who would be able to understand this on a deeper level. And as our confidence in the Dhamma gets deeper and deeper and deeper, so our confidence in the Buddha becomes deeper.