Jeremiah Covenant is owner of the Covenant Estate and last surviving member of the Covenant family. When he was a child, Jeremiah found a strange occult book in his father Joseph's library. Jeremiah decided to play a game with his younger siblings by having them go to the Isle of the Standing Stones and participate in reading out an incantation found in the book. What began as an innocent game quickly turned to terror when they accidentally unleashed an evil presence which in turn cursed the siblings.
As the children grew up, their personalities became evil and twisted, until one by one, the four younger siblings succumbed to different forms of madness, disease, and death. Before the last of his siblings died, Jeremiah went off to fight in the Great War, where he met and befriended a man named Patrick Galloway, who became his trusted friend and comrade. Jeremiah was the commanding officer of Patrick's unit, which was dedicated to soothing the fears of the superstitious soldiers. When the unit was attacked by a Trsanti war band lead by a Shaman, Patrick shot the Shaman just as he released a blast of energy from the mysterious crystal in his hand. Patrick passed out and woke up in a medical tent recovering from severe burns. Jeremiah had brought Patrick to medical attention, saving his life, and left Patrick the Shaman's crystal - the Gel'ziabar Stone - as a souvenir. Because of this, Patrick had felt ever since that he owed Jeremiah his life.
After returning from the war, Jeremiah contracted a terminal form of cancer, and feared that if he, the last Covenant, died, then the mysterious evil the children had tapped into below the Standing Stones would be unleashed, freed to destroy the world. Worse yet, rumours had begun to circulate that his four siblings had risen from the grave as malevolent abominations.
On April 1923, Jeremiah sent a letter begging Patrick to return to Ireland and investigate the strange happenings on the Covenant Estate. Because of Patrick's nomadic lifestyle, he did not actually receive the letter for months afterwards, and only finally made it to the Estate a six months later, at some point in October 1923. By then, Jeremiah was bedridden, and his undead siblings were seemingly hellbent on infiltrating the Covenant Manor and murdering him. Once Patrick arrives at the Estate, Jeremiah fills him in on what has happened prior to his arrival, and begs him to investigate, to find a way to put his brothers and sisters to rest, and break the curse once and for all.
After Patrick obtains a mysterious weapon somehow tied into the curse, the Scythe of the Celts, and uses it to slay Jeremiah's sister Lizbeth, Jeremiah is held hostage by his brother Ambrose in an attempt to obtain the Gel'ziabar Stone. Thinking if he gives Ambrose the Stone he would spare his brother's life, Patrick hands over the Stone, but Ambrose quickly beheads Jeremiah, before being killed himself by Patrick.Grieving for Jeremiah and driven by fury, Patrick hunted down the last two remaining siblings in order to avenge his friend and stop the Undying King, a mysterious entity that the siblings seemed to serve. After Patrick kills off Jeremiah's undead siblings he finds out that Jeremiah is in fact still alive. He actually died during the war on the day that Patrick killed the Shaman; he was brought back to life by the curse and thus proceeds to put his plan into motion. He lured Patrick to his Estate under the impression that he was very ill and was afraid his siblings are trying to kill him. Jeremiah wanted Patrick to kill off his undead siblings using the Scythe of the Celt, because with all four of his siblings dead, Jeremiah was the only link remaining to the Undying King. Jeremiah intended to kill Patrick, take the Gel'ziabar Stone, and use it to siphon away the power of the Undying King, which would make him powerful enough to remake the world as he saw fit. Instead, Patrick casually decapitated Jeremiah with the Scythe. Although this put an end to Jeremiah's evil plan, it also finally broke the seal, and the Undying King rose from the soil of the Isle of the Standing Stones, with only Patrick standing between it and the destruction of Humanity.