The Red Hulk is the name of two characters in the Marvel Universe.
General Thaddeus "Thunderbolt" Ross was the first person to take on the identity of the Red Hulk. The first incarnation of Red Hulk (also known as Rulk) first appeared in the Hulk series that debuted in 2008. The 2010 "World War Hulks" storyline reveals that this being is United States Army General Thunderbolt Ross, the father-in-law and longtime nemesis of the original Hulk, Bruce Banner. The storyline reveals that Ross was given the ability to transform into Red Hulk by the organizations A.I.M. and the Intelligencia, and that he did this in order to be able to better fight the original Hulk.
Appears in Avengers EMH and Hulk and the agents of SMASH.
The origin of the second Red Hulk appears in the 2017 debut issue of U.S.Avengers. Four-star General Robert Maverick is selected for his genetic profile to create a being who is "halfway to a hulk." A device called the Hulk Plug-In, created by Avengers Idea Mechanics (a legitimate technology company created from the remnants of the defunct supervillain organization Advanced Idea Mechanics), is implanted in Maverick's wrist. When triggered, it turns him into a variation of the Red Hulk for one hour approximately every day and a half. Unlike the Thunderbolt Ross version of Red Hulk, Maverick retains his mustache in his Hulk form and wears his sunglasses. He joins the U.S.Avengers.