His dæmon was Stelmaria, a snow leopard. The name Stelmaria is probably derived from Stella Maria or Stella Maris, a pseudo-Latin phrase, with the meaning of "star of the sea". In case it is derived from Italian, its meaning approximates to "Star Mary". In this case, it is probably associated with Bethlehem and the Nativity.
Lord Asriel was a highly respected member of the British aristocracy. He was an explorer, and did work in experimental theology, through which he acquired much power, land, and money. But when he had an affair and child with a politician's wife, this changed. The woman's husband, Edward Coulter, came after him and his daughter Lyra. Lord Asriel challenged and killed him. When the church found out, he was taken to court and lost all his money and property, and Lyra was sent to a convent. Lord Asriel, who hated the church, rode in one day and took her away to his old alma mater, Jordan College, where she was placed in the care of The Master, growing up under the belief that she was the orphaned daughter of Lord Asriel's recently deceased brother, Count Belacqua.
After travelling to the North, Lord Asriel visited Jordan College and was almost poisoned by the Master, who read his alethiometer and found that Lord Asriel's actions would be dangerous. Lord Asriel was saved by Lyra, who saw the poisoning of the decanter. He managed to gain money for an expedition using photograms of Dust and a city in the sky as well as the shock value of a decapitated head which he claimed was Stanislaus Grumman's. He traveled to Svalbard but was imprisoned and guarded by the panserbjørne under Iofur Raknison on the orders of the General Oblation Board, one of his enemies, run by his ex-lover, Mrs Coulter. He managed to get hospitable treatment and waited for a child on whom to perform intercision in order to open a window in the aurora with the help of witches. Eventually a child arrived: Roger Parslow, brought there by Lyra.
He entered Cittàgazze and, after a battle, allied himself with the rebel angels under Xaphania. He travelled to an empty world and built an enormous basalt fortress, gathering armies from many different worlds in order to start his rebellion against the Kingdom of Heaven. Ruta Skadi found him and he told her his plan, also getting her clan's support in the war.
Later, he had his friend King Ogunwe and Lord Roke of the Gallivespians attempt to find Lyra, the second Eve, from Mrs Coulter. They captured Mrs Coulter, but Lyra and Will escaped with two of Lord Roke's agents. Lord Asriel then attended to Mrs. Coulter and tried to influence Lyra and Will, as they held the key to renewing the Dust flow. Lord Asriel let Mrs Coulter escape in an Intention Craft and had Lord Roke follow her to gain information from the Consistorial Court of Discipline. They found that the Church made a bomb to kill Lyra and Lord Asriel rescued Mrs Coulter just in time, as well as destroying Saint-Jean Les Eaux a moment too late with his intention craft.
Lyra survived, and Lord Asriel had his army search for her and Will's dæmons so that the Authority's armies couldn't control them. Lord Asriel found that the bomb blew a hole under all the worlds into the Abyss and came up with a plan to take down the Authority's powerful Regent, Metatron. As his army fought the armies of the Authority and the Church, Mrs Coulter tricked Metatron into trying to kill Lord Asriel and take Lyra's dæmon as he was on the edge of the Abyss. Lord Asriel and Mrs. Coulter sacrificed themselves by taking Metatron down with them, falling in the Abyss as ghosts for eternity.
Presumably, the name Asriel may be a derivative of the Hebrew "Asra'el". In the Jewish and Muslim tradition, "Asra'el" is the Angel of Death, and separates the soul from the body at death. According to another theory, "Asra'el", a homonym for Israel, may refer to the English translation of the name Israel — the name given to Jacob in the Hebrew Bible: "He who has struggled with God". Sometimes the name, Azrael, although incorrectly, is associated with Satan and Demonology, probably due to Asriel's battle against The Authority in the trilogy.