This one I believe to be a male--it has a slightly larger horn, and more robust jaws, than the other individual closely associated with it. Length about 35 mm.
I found a pair of these beetles under the bark of a rotting log. I tore the log up looking for the larvae, which I have never photographed, but had no luck. Having captured a pair, I'm going to try and rear them. (I felt a bit guilty about tearing up the log, too, disrupting their home--I normally do nothing more than pull off a bit of bark.)