Thanos' history is presumably similar to his Earth-616 counterpart's. During one of his schemes, which involved the Infinity Stones, he was turned to dust and apparently died. Thanos eventually returned from death and now wore the Infinity Stones as rings on his right hand. He traveled to Earth and was intercepted by Dr. Spectrum who expressed shock that Thanos was back. The pair then battled each other.
Powers and Abilities
The way Thanos' Infinity Rings project differently colored constructs could be a pastiche of the power rings of the various Lantern Corps, where Green Lantern gets his power from and who Doctor Spectrum is based on. Thanos himself is possibly a pastiche of the Green Lantern villain Sinestro.