This is my summary of how Smog (my primary Fallout 3 OC) befriended Dust, her Deathclaw Companion. The poor thing was exiled from its pack when it was just a pup because of its missing horn (technically half), thus making it appear 'weak' or unsuitable as a potential pack leader. Eventually, while it was scavenging for food, is right arm was caught in a Raiders' bear trap. The young male screamed and cried and tried everything to remove it, but to no avail.
Smog's ref sheet:
Deathclaws/ Fallout (c) Bethesda
Smog, Dust/ Art (c) Me