As a Lord of Order, Nabu 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, as he needed a permanent host to keep Klarion at bay. Zatara convinced Nabu to take him as a host instead of his daughter.
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.