History
The Leader became the Hulk's arch nemesis after being exposed to the same gamma radiation that created him. With the massive intellect Leader possesses he has become obsessed with destroying Hulk.
Doorway to Destruction
It was revealed that the Leader was the one who supplied the mind-control technology to Annihilus. At the end of the episode, it was shown that he had planted Skaar on the Agents of S.M.A.S.H. to learn about them, in exchange for Leader telling Skaar about his past.[1]
Hulk-Busted
Leader hijacks the Hulkbuster armors to fight Hulk's team. Leader makes himself known on a holgram where he magnetizes the Hulkbusters into one giant Hulkbuster where it captures Iron Man. Leader uses another hologram stating that he has rigged the giant Hulkbuster to explode and blame the destruction of the city on Iron Man and the Agents of S.M.A.S.H. After the giant Hulkbuster was defeated, Hulk is shown to be aware that Leader is using Skaar after viewing the security footage of their base and tells A-Bomb that he has plans to manipulate Skaar into "giving them Leader."[2]
The Incredible Shrinking Hulks
Leader uses a shrink ray placed in a miniature golf course section to shrink the Agents of S.M.A.S.H. Leader then contacts the Agents of S.M.A.S.H. where he mentions that he has shrunken them in his plot to crush them like ants. Leader later arrives where the truth between Leader's connections with Skaar and Skaar's lost memories is revealed where Leader restores Skaar to normal size. Leader then attacks the Agents of S.M.A.S.H. whee he states to them that he has promised their destruction. Skaar then makes his choice where he grabs Leader and goes on the attack enough for the Agents of S.M.A.S.H. to be freed from Leader's mental attack. The Agents of S.M.A.S.H. go on the attack and defeat him. When Skaar states to Leader that Earth is his home, Leader escapes as he charges the shrink ray to go into overdrive to shrink the entire golf course. [3]