Ok, my theory is actually that he is sometime in the future because at the end of hl2 ep 1, he auses time to put you into stasis again, he has some relation to Freeman because he was there in hl1 and in hl2 all the way but said very little. this could be implying that he may be important to the...
Just a thought... Maybe he is just a teleporting, inter dimensional bureaucrat who has ties with the Xen world and human world and was really bored on a Sunday with nothing but golf on the tele. I mean honestly, get real guys!