Khn'nr is a fictional alien character who has appeared in numerous comic book series published by Marvel Comics. He is a Skrull sleeper agent posing as the Kree Captain Mar-Vell (also known as Captain Marvel).
The shapeshifting Skrull Khn'nr was bonded with the DNA of Mar-Vell to lock his body into Mar-Vell's form and given technological replicas of the Kree Nega-Bands. However, his mental conditioning was botched, causing Khn'nr's personality to be erased and leaving the Mar-Vell persona dominant. Though part of the Skrull invasion of Earth, this Captain Marvel decides to fight against the invading Skrulls.
In 2007, Mar-Vell supposedly returned to the Marvel Universe during Marvel's Civil War crossover storyline. He made his appearance in the "Civil War: The Return" one-shot, in a story written by Paul Jenkins. It was later revealed that this was in fact a Skrull named Khn'nr during the 2008 Captain Marvel mini-series, which spun out of the events of his Civil War appearance.
As part of the Skrull Secret Invasion, a shapeshifting Skrull called Khn'nr was locked into the shape of Mar-Vell, the first Captain Marvel and given technological replicas of the Kree Nega-Bands to replicate Captain Marvel's powers. Khn'nr received memory implants to turn him into a sleeper agent making him believe he was Captain Marvel supposedly up until the time of the invasion when a psychological trigger would be activated to return him to his Skrull persona.
The real Mar-Vell died of cancer so to explain his comeback from death, a false memory was implanted in the Skrull Mar-Vell to make him believe he had encountered a wrinkle in space-time in the past, supposedly caused by Tony Stark, Hank Pym, and Reed Richards' construction of a prison within the Negative Zone, which Captain Marvel touched and was transported through time to the Negative Zone in the present day. Initially unsure of how to approach the situation, the Earth's heroes revealed Mar-Vell's history to him but also offered him a place in this new future as a warden for their prison, at least until, as the Sentry implicated, Mar-Vell would return to his past.
He is later called in to help the pro-registration heroes who revived him, in the final battle of Civil War; however upon seeing the chaos they are causing, he departs, to France, where he spends all of his time observing a painting of Alexander the Great in the Louvre and contemplates Alexander's similarities to himself. This painting was meant to be his psychological trigger, but due to an error in the methods of Skrull scientists, Mar-Vell retained his personality and memories prior to his Skrull captivity in their entirety. Most of Khn'nr's personality had accidentally been erased as a byproduct of the botched mental conditioning. Consequently, the Mar-Vell persona remained defiantly dominant.
When the Skrulls realize what had happened, other Skrull agents posing as supervillains Cyclone, Cobalt Man, and a team of Kree soldiers unsuccessfully attempt to capture Captain Marvel.
When he learned the truth and became fully aware of his true identity he decided to embrace Mar-Vell's memories and rebel against the Skrulls and protect Earth from their invasion. However, at the same time that Skrull infiltrators strike S.H.I.E.L.D., S.W.O.R.D., the Baxter Building and a number of Stark Enterprises facilities, Captain Marvel launches an attack on Thunderbolt Mountain, deciding that he can destroy some of the things he sees as problems in the world, like the Government sanctioned supervillains Thunderbolts, during the initial strike of the Skrulls' invasion. He defeated the Thunderbolts, leaving Norman Osborn to convince Khn'nr that only he can decide who he really is, which leads Khn'nr to attack the Skrull armada. He destroys many of the fleet but is attacked by a Super-Skrull and it nearly kills him.
Barely alive after his effort, he manages to crash back on Earth, crossing Noh-Varr's path, who briefly mistakes him for the original Mar-Vell. Before dying from his wounds, Khn'nr spurs Noh-Varr into continuing Mar-Vell's legacy as the protector of Earth, branding with his dying words the Skrulls as liars and traitors and asking that Noh-Varr defeat the Skrulls and take on the mantle of Captain Marvel, which Noh-Varr does, joining the Dark Avengers under that name.
Though a Skrull, Khn'nr has the memories, knowledge, and skills of the Kree, Mar-Vell; presumably including Mar-Vell's Kree military training giving him mastery of all forms of Kree unarmed combat, as well as extensive knowledge of the technologically advanced vehicles and devices of the Kree Empire. It is unknown if the botched mental conditioning has left Khn'nr any of his previous Skrull knowledge.
The Skrulls also developed technological replicas of the Kree Nega-Bands, though it is unknown if these work in the same fashion as the Kree version which converted Mar-Vell's psionic energy into strength, a high degree of imperviousness to harm, the ability to project force blasts, survive in space and the power to fly at faster-than-light speeds, the bands do give him exactly the same powers. They are also fully compatible with the originals, as seen when Ms. Marvel, armed with the original Nega-Bands is able to banish him in the Negative Zone by clicking her wrist on his.
The main stories where the character was introduced have been collected into a trade paperback:Captain Marvel: Secret Invasion. Marvel Comics. TPB: February 2009. ISBN 978-0-7851-2422-1. HC: August 2008. ISBN 978-0-7851-3303-2.
Collects: Captain Marvel (vol. 6) #1-5, Civil War: The Return