[math-fun] Dumb astronomy question

The earth's axis is inclined ("axial tilt") at approx 23.5 degrees to its orbit around the Sun. How did it get that way? If most of the stuff in the solar system originally had the same axis of angular momentum, then wouldn't the earth most likely end up with a zero degree axial tilt? What is the current best explanation for the tilt? Did the earth get hit by another body from an odd angle -- e.g., when the Moon was formed? Wouldn't tidal forces eventually get rid of the tilt? Thanks in advance for any pointers.