Prior to the events of the story Marley and Marley acted as partners to Scrooge and shared his selfish outlook on life, only it was implied that these two ghastly gentlemen were far worse than Scrooge in their inhumanity towards their fellow man: some of their horrid deeds in life were evicting an entire orphanage and taxing the poor unfairly and without mercy.
However in death the two greedy villains were imprisoned in a type of purgatory, doomed to carry the chains of their sins for all eternity - such a fate was also reserved for Scrooge himself if he had not changed his ways, a fact the two ghosts vividly warn him of.
During their famous song Marley and Marley introduce themselves as "avarice" and "greed" while detailing all the terrible things they had done as mortals and how it had condemned them as spirits, warning Scrooge that he would soon follow if he didn't change his ways - they then departed, telling Scrooge that he would soon be visited by three spirits.
Jacob Marley was played by Statler, and Robert Marley was played by Waldorf.
In the book, there was only one Marley, and that was Jacob. The Jim Henson company just made it two Marleys as brothers so both Statler and Waldorf could play the role.Robert Marley was given that name to be similar to Bob Marley.