He appears to have been the uncle of the young womanJohn Marston meets when he is searching Blackwater for survivors of the plague. The woman advises Marston to burn the undead at the cemetery where Mordecai is buried, telling John to burn her uncle "real good" and put an end to the infected rising from the grave.
It appears that Mordecai may have abused his niece at some point during his life, as she seems very angry when telling Marston to "burn him real good." Also, while rising from the grave he utters the phrase "Ain't you sweet, little lady," indicating that he may have tried to sexually assault her. This is further proven by his tombstone listing him as an "exuberant family man."
His tombstone reads: Mordecai Robbard. Exuberant family man. Sorely missed. 1861-1908.
He is the first bruiser zombie encountered by Marston in the storyline.
He is also the first boss zombie encountered.
"Mordecai" means "Little One" in Hebrew. This is ironic, considering his large size.
It is possible that Mordecai died of smallpox since his date of death is set at three years before the game. His niece tells Marston that her mother died three years ago from the same disease. There may well have been an outbreak which spread through the Robbard family and killed several of its members.
After downloading Undead Nightmare, his grave can also be found in the regular storyline.
His last name indicates he is of Welsh or Scottish descent.
His bruiser model can be found everywhere as an enemy in Undead Nightmare. He is even seen attacking Nigel West Dickens before he is killed by John in "A Cure for Most of What Ails You."