Rock is a Crypt ganger, and one of the two guards that stand at Scrapheap's entrance in the demo version of the original Fallout - the other one is Skizzer. He can direct you to the rest of the Crypts when he is talked to and asked about them.
If the player character talks to him while unarmed, he can be asked about either Scrapheap or the gang called Crypts running the town. Talking to him again will make him respond annoyingly that Stone asks too many questions and dismisses him.
If the spoken to while armed, he will direct them to the locations of the Crypts in all dialog choices. If one joins the Fools, he will tell them that they've made a big mistake. Alternatively, if one sided with the Crypts, he will respond positively.