Hathor Maat was the Captain of the 3rd Fellowship of the Thousand Sons Space Marine Legion during the Great Crusade. Maat was also the Magister Templi of the Pavoni. He escaped the Burning of Prospero as part of the contingent teleported from the planet by Magnus to the Eye of Terror.
Like his fellow captains, he had secondment with another legion. He is known to have spent time serving with the Emperor's Children Legion. Maat was noted to be exceptionally proud of an Oath of Moment attached to his breastplate. It had been personally carved by Fulgrim himself. [1b]. He was described as being vain and proud[1c] yet exceptionally handsome and stereotypically heroic looking with golden hair. [1d]
He was the Magister Templi of the Cult of Pavoni[1e] and a powerful psyker whose abilities focused primarily on the ability to heal [1f] although he was also known to have the ability to channel potent offensive lightning spells. [1g]. Maat was present with the Legion while serving as part of the 28th Expeditionary Fleet. And took part in the campaigns on Aghoru and Ark Reach Secundus. He participated in the failed defence of Prospero and was last noted to be present amongst the surviving members of the Thousand Sons who escaped to the Planet of Sorcerers.[1h]
Maat accompanied Ahriman on his quest to track down the Shards of Magnus. However, he began to suffer from the flesh change. Striking a bargain with the Daemon Aforgomon and Lucius accompanying Ahriman's cabal, Hathor Maat learned to hold off the flesh change by sacrificing captive humans. Aforgomon further manipulated Hathor Maat into altering a single line of the Book of Magnus. However when Ahriman's cabal finally came to the shards of Magnus at Nikaea, the change began finally overcame Maat. Paying the price owed to Aforgomon, Ahriman sacrificed Hathor Maat to allow the daemon to take over his body and manifest as the Fatewoven (which as it seems was the same Kairos Fateweaver in disguise, as well as Aforgomon). 
Hathor is a major goddess in ancient Egyptian religion. She was, amongst other roles, the mother or consort of the sky god Horus and the sun god Ra and symbolic mother of their earthly representatives, the pharaohs. She also crossed boundaries between worlds, helping deceased souls in the transition to the afterlife. Maat likewise is an Egyptian goddess and personifies the concepts of truth, balance, order, harmony, law, morality, and justice. She also regulated the stars, seasons, and the actions of mortals and the deities who had brought order from chaos at the moment of creation.
- 1: A Thousand Sons (Novel) by Graham McNeill
- 2: The Crimson King (Novel) Ch 23
- 3: Warhammer Community: Artwork of Prospero (20/11/2016) (last accessed 3 June 2019)