Mr. Gillis is the father of Mary and Jamie. He disapproved of Mary's romantic relationship with Arthur Morgan due to him being an outlaw. He has become verbally abusive towards to his children, and became addicted to alcohol, whoring, and gambling. He has also started pawning off his family's valuables, likely to pay off his debt.
Events of Red Dead Redemption 2
Mary worries for her father's strange behavior and enlists Arthur's help in investigating. Arthur is reluctant to help, but if he accepts he takes Mary to see Mr. Gillis. After a one-sided heated exchange with Mary, Mr. Gillis storms off and is tailed by Mary and Arthur. It is revealed that Mr. Gillis intends to sell the brooch Mary's deceased mother had given her for money. Mary, angered at this, confronts her father, who is surprised to see her and is angered to see Arthur. After Arthur takes back the brooch from a loan shark named Ashton and returns to Mary, she reveals that Mr. Gillis had left and waves off Arthur's offer to look for him, stating she no longer cares wherever Mr. Gillis went.
Some time later in the epilogue, Mr. Gillis' corpse can be seen on a dirt road just beyond Coot's Chapel in New Austin, being picked at by vultures. His corpse can also be visited and is flagged as a "Stranger".
Mr. Gillis is shown to be self-absorbed, irritable, and an uncaring individual. Mary states that he wasn't always like this, but this could be biased due to her more lenient and honeyed views on her family. He's noted for being hypocritical by Arthur. As while Arthur is an outlaw whom Mr. Gillis mocks as a killer and a thief, Mr. Gillis is a whore-mongering alcoholic who gambles often, and is said by Arthur to be a bully and a coward. He is shown to be verbally abusive to Mary, and Jamie confirms that he has undergone similar treatment. His lack of care for his family becomes more apparent when he tries to pawn off the brooch his wife passed down to Mary.
Mr. Gillis is an overweight old man with a pronounced belly. He has gray hair and always seems to be red faced from heavy drinking.