Nighthawk was a member of the Squadron Supreme.
He is seen in a flashback in the episode "Hyperion" where is shown as part of the Squadron Supreme on Hyperion's home world, but is stated to have died alongside the rest of the team.
This is proven false when he appears in the episode "Nighthawk" when he first appears in the disguise of S.H.I.E.L.D. Agent Kyle Richmond. Using his position on S.H.I.E.L.D. as the Director of Interstellar Operations, Kyle secretly gets into S.H.I.E.L.D.'s database in order to obtain the contingency plan about the Avengers. The Avengers managed to get out of their traps and help Falcon to fight Nighthawk. While Hulk and Thor work to shut down the citadel, the others fought Nighthawk where they managed to defeat him and remand him to S.H.I.E.L.D. custody. Outside of Nighthawk's cell, Nick Fury mocks the idea of Nighthawk being one step ahead where Nighthawk states that he's always one step ahead. This is proven right when Hyperion arrives and frees Nighthawk in front of Nick Fury. Nighthawk and Hyperion then leave to get their group together.
In the episode "Dark Avengers," Nighthawk obtains the Reality Infinity Gem and uses it to make the Squadron Supreme superheroes and the Avengers the bad guys. Upon seeing the differences, Iron Man rallies the Avengers into claiming the Reality Infinity Gem and causing the Squadron Supreme to retreat.
In "Terminal Velocity," Nighthawk sends Hyperion to fight the Avengers as part of a diversion for Speed Demon to get specific information from the Stark Tower computers. After Hyperion and Speed Demon get away from the Avengers, Hyperion and Speed Demon meet with Nighthawk at the Squadron Supreme's hideout where Speed Demon gives Nighthawk the information he obtained.
In "Spectrums," the Power Prism that possessed Doctor Spectrum made its way back to Nighthawk. Upon the Power Prism no longer needing a host, the Power Prism forms a new body that resembles Doctor Spectrum as Nighthawk welcomes it into the Squadron Supreme.
Later in "Midgard Crisis," Nighthawk learned from Zarda that her plans to sway an Avenger to their side didn't go well and that she was wrong.
In the episode "Avengers' Last Stand," Nighthawk puts his plan into motion which ends with the restoration of Nuke and the apparent destruction of the Avengers. With a defeated Thor in the Squadron Supreme's custody, Nighthawk makes his demands on television stating that Earth is under the protection of the Squadron Supreme. In the episode "Avengers Underground," Nighthawk divides the Earth amongst the other Squadron Supreme members. After most of the Squadron Supreme are defeated, Nighthawk teleports Nuke and Hyperion to the tower where he has Hyperion absorb Nuke's powers with the intent on destroying Earth. As Nighthawk prepares to leave Earth, Iron Man defeats him and the rest of the team stops Hyperion from reaching the planet's core. Nighthawk and the rest of the Squadron Supreme are later mentioned to have been remanded to a special wing of the Vault.
Powers and abilities
Nighthawk is a superb athlete and possess super-strength and increased agility and durability from dusk till dawn. He has also used several costume aids, such as a jet-powered artificial wing system, artificial claw tips, lasers and projectile weapons.
As the Squadron Supreme were based on DC Superheroes, Nighthawk is the SS version of Batman. His voice actor for Avengers Assemble also voiced the Dark Knight in Beware the Batman.