Major Story Arcs
Tribulus's homeworld of origin is unknown and he was first seen accompanying the bountyhunters Amon Hakk, Skwaul, and Getorix in pursuit of Vril Dox, aka Brainiac 2, to collect the bounty on his head. Getorix, a cyborg, had mental control over the physically powerful but mentally primitive Tribulus thanks to an implant at the back of his head, which acted like a remote control. During their time on Earth (where Vril had fled), Tribulus served as their muscle, displaying incredible feats of brute strength and raw power (so much so in fact that not even Supergirl, a Kryptonian, was able to hold her own against him). Tribulus ceased to be a threat to Brainiac 2 when he tricked Amon into shooting Getorix in the back, disabling him long enough for Dox to steal his remote implant and have Supergirl implant it at the back of his head, thus giving him complete control over the beast. Dox then showed his gratitude toward Supergirl for saving his skin by having Tribulus knock her out cold with a blast of mental lightning, his reasoning for betraying her being that he knew she'd never allow him to keep Tribulus after all the trouble it had caused since its arrival on Earth (and its obvious potential as a lethal living weapon). Tribulus has since served as the muscle on Dox's new R.E.B.E.L.S. team, the beast usually sleeping in his ship's cargo hold so as to not risk damage to the craft.
Powers & Abilities
Tribulus possesses unfathomable levels of sheer brute strength, easily outclassing even Kara Zor-El, a Kryptonian living under a yellow sun, and likewise has high levels of invulnerability (limits of which are unknown, but Dox seems to have utmost confidence in its ability to handle itself, going so far as to leave the beast alone to guard his ship. when he and Wildstar left in search of Strata, and giving his "condolences" to anyone unfortunate enough to stumble across his pet). He also has the ability to generate powerful bolts of electricity from his head, presumably produced by his brain in a similar fashion to the superhero Static (only far more powerful and wild, since it was enough to do serious harm to Supergirl). There are two lines or indents, presumably electrical organs of somesort, that light up when the lightning bolts are fired. Tribulus is a very primal and animalistic creature, running wild and attacking anything in its path when not under someone else's control, and its mercilessness towards others and its unquestionable loyalty to whoever wears the implant is what makes him so valuable to Vril Dox's campaign to retake L.E.G.I.O.N.