Cloak and Dagger (Marvel)

Cloak and Dagger (real names Tyrone "Ty" Johnson and Tandy Bowen, respectively) are a pair of young superheroes, one controlling darkness and the other controlling light, whose complementary powers help cover each other's weaknesses. They are characters in the Marvel Comics Universe.

The Avengers: Earth's Mightiest Heroes
While Dagger never made an appearance Cloak can be seen on Fury's wall of Skrull suspects in the episode "Infiltration".

Ultimate Spider-Man
Dagger was among the wave of rising young heroes S.H.I.E.L.D. was looking to recruit, however they had no intent with Cloak due to his temperamental attitude. In the episode "Cloak and Dagger", Cloak fell into the control of the demon Dormammu, who used him to kidnap various mystics and brainwash them to help create a portal for his army to invade Earth. After Cloak kidnaps Iron Fist, Dagger joins with Spider-Man to find him.

They are able to discover Dormammu as the culprit and follow him to his Dark Dimension via Doctor Strange's Eye of Agamotto but confront Cloak as resistance from further passing. Spider-Man is able to bring Cloak back using Dagger's light daggers to exonerate Cloak from Dormammu's influence. The three encounter the brainwashed White Tiger, Iron Fist, and Doctor Strange and are forced to fight them; Dagger aids in breaking the spell over them with her powers. But before she can free Doctor Strange, Dormammu arrives and attacks them, forcing them on the retreat. Fortunately, Cloak uses his powers to help Dagger get close enough and frees Doctor Strange, who then helps the group escape the castle with Dormammu on their trail.

Cloak offers to get everyone safely back to Earth despite Dagger's worry, but when everyone escapes through, he is halted from teleporting himself by Dormammu, causing him to become trapped between two dimensions and allowing Dormammu access. Spider-Man dons the Eye of Agamotto to temporarily incapacitate the demon while Doctor Strange banishes Dormammu back to his dimension. Spider-Man offers the two to join S.H.I.E.L.D., although the two state they will consider it. After departing, they are revealed to be working for Taskmaster who took them in and gave them shelter beforehand, and makes them turn against the notion of joining S.H.I.E.L.D.

In "New Warriors", they aid Taskmaster as a part of his "Thunderbolts" team in busting out Green Goblin, Beetle, Doctor Octopus, and Scorpion of the S.H.I.E.L.D. Helicarrier, incapacitating Spider-Man's team and battling against Spider-Man, Agent Venom, Amadeus Cho, Ka-Zar, and Zabu in the midst of the endeavor. However, when Cloak is nearly killed by the Helicarrier's fans, Taskmaster leaves him to perish while revealing his manipulation of the two to a disillusioned Dagger and departs them. Spider-Man manages to save Cloak and convinces the two into joining the New Warriors instead, and amend for their actions by defeating and apprehending the escaped supervillains.