A Thane has two sons, and at the age of 15 they are told the truth of the Brethren. One will rise to become the new Thane, while the other will be driven mad with the Truth. Thane Ector is the most recent of the Brethren to hold the title Thane, while his brother is now simply known as Fool.
Thane Ector makes his first appearance in Avengers #334, which was written by Bob Harras.
The Celestials, creators of both the Eternals and the Deviants on Earth, later created the Brethren. The Brethren were formed not from humanoid forms like the previous creations, but instead from bacterial life from the planet Omega Climion Six. The Brethren were used as a weapon of Arishem the Judge, who would determine if a planets life forms were worthy. If Arishem found them unworthy, he would send the Brethren in to eradicate all life on the planet. For an unknown reason the Celestials eventually left the Brethren to wander the Universe, but they were eventually found and captured by the Collector.
Thane Ector became the most recent leader of the Brethren, though it is unknown how long the Brethren live, it is believed that he was born and raised only inside the Collectors miniature eco-systems which the Collector. On his 15th birthday he and his brother learned the truth of the Brethren's origins, and from that point, are the only two of their people to know the truth. The Thane and his now insane brother are to keep the secret of their people, and also pass on great stories of their race to hide the truth. They explain their race as one of great warriors, sent out to the stars to conquer. They keep their fabricated history written on sacred scrolls, which no outsider is ever supposed to read.
As the leader of the Brethren, Thane Ector and his people seemingly escaped the Collectors ship and crashed it on the Blue Side of the Moon, where they ran into the Inhumans along with Quicksilver, and eventually into the Avengers. Once Thane Ector learned of Earth he left the battle, and headed to the planet that had been said to be the first to defeat Galactus. Thane Ector was accompanied by two other Brethren, the first being his second in command, Sybyl Dorn, who was also said to be his betrothed. The second one by his side was a creature named Fool, who was later revealed to be the brother.
Once on Earth Thane Ector continued to lead the his people in his conquest of Earth, and even placed his citadel upon the World Trade Center in New York. Many heroes opposed the Brethren, but the most prominent was the Avengers, with Captain America leading the charge. The Avengers stood little chance against the powerful forces of the Brethren, and Thane Ector easily defeated Captain America and then took Sersi captive. Something drew him to Sersi, and he actually revealed that his people were also created by the Celestials, and had the Sacred Scrolls of his people taken to Sersi so she could learn of his people. The Brethren looked to be on the verge of defeating Earth when it was revealed that the entire thing was a plot by the Collector. They had not escaped the Collector's ship, he had let them go, and wanted them to destroy Earth, leaving the last of the people on Earth to become part of his collection. The Collector then revealed the truth of the Brethren, that they were created from Bacilli, Sprilla, and Cocci, and were nothing more than a plague, and a tool of the Celestials and now the Collector.
The Collector destroyed the bodies of the Brethren, leaving only the base bacteria, mindless to float around and destroy everyone in their path. Sersi, realizing that Thane Ector and his brother Fool had a telepathic link with their people and she helped the two brothers reach out to the scattered Brethren. They scattered Brethren suddenly came together and formed a Uni-Mind, and they attacked the Collector. This destroyed the Brethren, including Fool and Thane Ector, who thanked Sersi with his final breath for helping them destroy their oppressor and finally doing something good.
Thane Ector possesses super human Strength and endurance, the extent of which is unknown. He has also shown super speed that allowed him to once best Quicksilver, though Quicksilver was slightly injured when this occured. Thane Ector also has the ability to shoot a powerful blasts from his eyes. Like all Brethren Thane is a sort of shape shifter and is able to absorb energy by sapping all the bacteria from any living being to make himself stronger.