As a Lord of Order, Nabu/Fate places order above all else, which often results in morally questionable decisions such as trying to permanently take children as hosts regardless fo their lives outside. However, occasionally Nabu will show kindness toward others, such as allowing Zatara and Zatanna one hour a year to speak. It is hinted that part of Fate's disposition is due to sitting on a shelf for decades at a time.
Doctor Fate is always manifested as the current host wearing the same uniform. The uniform consists of a golden helmet that covers the entirety of the host's head, excluding the ears and, occasionally hair, if it should be long enough. Fate wears a long, high collared cape, fastened with two large buttons. Beneath is a blue shirt with a golden oval set in the chest. He also dons a large golden belt with a circle in the center, and deep blue pants with golden boots.
Nabu was once a human that lived in Ancient Babylonia and was the son of Vandal Savage, then going by the identity of the "demi-god hero Marduk". Nabu and his sister fought alongside their father as they were confronted by people that were controlled by Starro. However, Nabu fell in the midst of the battle.
At some point after his death, Nabu became a Lord of the Order, and had to rely on human hosts to have a presence on the physical plane. He could take over host bodies when they wear the Helmet of Fate, transforming them into Doctor Fate. While he is in control, the souls of his hosts remain within the Helmet, powerless to influence the outside world.
Nabu gained a new human host when Wally West put on the Helmet in the fight against Klarion. They were evenly matched, but Fate won after he hurt Klarion's familiar Teekl, severing his ties with the mortal plane. Nabu at first refused to relinquish control of Wally's body. Kent Nelson, who had been mortally wounded, and sucked into the Helmet along with Wally when the young hero put it on, convinced Nabu that Wally was not the right suitor to be the next Doctor Fate. He would keep the Lord of Order company until a suitable successor was chosen. The Helmet of Fate would reside in Wally's room in Mount Justice for safekeeping.
Zatanna used the Helmet to fight against Klarion. After she took him down, Nabu refused to give up her body, despite arguments from Kent Nelson. Nabu revealed he released Kent's soul to the afterlife, as he needed a permanent host to keep Klarion at bay. Zatara convinced Nabu to take him as a host instead of his daughter since he was better at magic. Nabu wasn't swayed until Zatara gave his word and Zatanna was released as her father took her place.
Doctor Fate attended the Justice League meeting to consider expanding its membership. During the meeting, Captain Marvel questioned whether Fate should inherit Zatara's seat in the League, because Fate coerced Zatara into letting him use his body. Re-evaluation of his membership was put to a vote, though Fate justified staying on the League by stating that he joined at Zatara's request so that the others could keep an eye on them.
The moment the trio made it back to the Watchtower, the Team ambushed them with cure-tech. Doctor Fate was tagged straight away, and after taking care of the other two, Zatanna attempted to remove the Helmet. She was electrocuted by the magics that held the helmet in place.
Doctor Fate made an agreement with Zatanna that he would leave Zatara's body every year for one hour, so that they could spend time together. Both father and daughter thought that agreement was not fair enough. Nabu said that they should be grateful that he allowed it at all. As promised Nabu left his host every year just for one hour.
Batgirl presented Fate with recordings of an ancient temple she and other Team members had found in Bialya. Fate translated the hieroglyphics, revealing an ancient ritual to cleanse a scarab. Unable to perform the human ritual himself, Fate began to prepare Zatanna to perform it, but it would take months for her to learn it and make it work in concert with her powers.
Mongul, an alien despot controlling a giant satellite called the Warworld, unleashed an attack on Earth, with Doctor Fate emerging from a portal and creating a giant magic portal to absorb a laser attack. Mongul fired missiles, but Rocket arrived and used a force bubble to protect Fate. Captain Atom, Captain Marvel and Green Beetle emerged from Fate's portal and they kept Mongul occupied until the Team snuck aboard the Warworld.
The Warworld May 26 post-12:35, UTCTime Zone
As Mongul increased his assault on Earth, Doctor Fate conjured an enormous protective shield as the other Leaguers took out as many missiles as they could.
Doctor Fate created a portal that allowed Captain Atom, Nightwing and Green Beetle to board the Warworld, where Nightwing asked Blue Beetle what happened to the rest of the Team. After a briefing, Fate created a portal to allow Green Beetle to take Blue Beetle home.
Doctor Fate joined 39 other heroes of Earth in a briefing in Metropolis. The heroes would use a computer virus provided by Lex Luthor to safely disable the Magnetic Field Disruptors causing the disasters. The heroes were paired off with another into twenty squads: one member would run interference against Beetle-tech Drones guarding the disruptors, allowing the other to get close enough to plant the virus.Doctor Fate was assigned to Mu Squad, and worked alongside Blue Devil.
Within thirty minutes, all squads had succeeded in their mission.
Nabu has no physical form, thus requiring a host in order to inhabit the reality of Earth. His magical connection to the Helmet of Fate allows him to completely possess the body of those that don said helmet. Once in control, he can utilize many mystical abilities including:
Nabu exists inside of the helmet of Fate. Without a host body, he cannot manifest as Fate and cannot affect the physical world. His power is also dependent on the host. As stated by Klarion when Nabu possessed Wally, Fate was weak because Wally had no affinity with or belief in magic. If Doctor Fate is injured when in battle, his host will also feel pain. Zatara also offered himself to Fate by stating that his magic was at its peak and his body fully developed on which Nabu agreed and chose Zatara over Zatanna.