Lothair Mantelar was a strict ascetic and proselytizer who lived during the War of the Hundred Years. His homeland and many of the details of his life are not known, but he is infamous in history as the founder of the Children of the Light.
Mantelar believed that the chaos of the civil war to seize control of Artur Hawkwing's Empire was allowing the Shadow to gain root and flourish amongst the people. He outlined his vision of the simple, humble lives that people should lead in the name of the Light in a book called The Way of the Light, which gained some popularity during those dark times, although its assertion that touching the True Source was provenance of the Creator alone and that any who dared wield the One Power were servants of the Dark One (including all Aes Sedai) was controversial. Mantelar founded the Children of the Light in FY 1021 as a preaching organization dedicated to spreading the word of the Light and to rooting out Darkfriends. Due to the ongoing military conflict, the Children found themselves having to learn how to fight to defend themselves, but as the decades passed the Children transformed from a simple preaching group to a militarized organization of crusaders. In FY 1111, presumably long after Mantelar's death, the group had formally become a military order dedicated to the destruction of Darkfriends and also the Aes Sedai.
Lothair Mantelar's name seems to be an allusion to Martin Luther, father of the Protestant Reformation.