Kevin Sydney is a fictional character appearing in American comic books published by Marvel Comics. The Changeling has been depicted as a member of the X-Men. Created by writer Roy Thomas and artist Werner Roth, the character first appeared in The X-Men #35 (August 1967). Kevin Sydney first appeared as Changeling, a mutant shapeshifter.
Proteus
Kevin Sydney, known as "Changeling", originally worked for the villainous organization Factor Three. He acted as the Mutant Master's second-in-command in an effort to trigger World War III. After successfully capturing the heroic X-Men, the Mutant Master is exposed as an extraterrestrial and goes out of control. The mutants of Factor Three ultimately joined with the X-Men to defeat the Mutant Master.  Following that group's defeat, Changeling sought to reform. He divulged to Professor X that he was suffering from an unspecified terminal illness with only a few months left to live and wished to atone for his misdeeds. Professor X recruited Changeling to act as a stand-in, unbeknownst to the X-Men, while the Professor isolated himself to prepare a defense against the alien Z'Nox's invasion. Changeling, masquerading as Professor X, led the X-Men's efforts to defeat the Subterranean Grotesk. He was mortally wounded in battle with Grotesk by the explosion of an oscillotron machine and, consequently, died preventing the destruction of Earth. The X-Men mourned the loss of Professor X until it was later revealed that it was, in fact, Changeling.  When the mystical Darkhold was recreated, Changeling's spirit used the opportunity to possess Meggan. Angry that he used his remaining time helping the X-Men instead of seeking a cure for himself, Changeling sought revenge against Professor X. However, Merlyn later admits that the encounter was merely fantasy, having orchestrated the event to prepare Excalibur.  Changeling again returned and battled She-Hulk when he was raised from the dead as a zombie by Black Talon to form part of the team X-Humed (which also consisted of Harry Leland, Living Diamond, and Scaleface). It is Changeling who is able to break Talon's control of him long enough to allow She-Hulk to win and lay the zombies back to rest.  Morph continued to be the heart of the team until a mission in which Mimic was taken over by a Brood egg. During the battle, he killed Sunfire. Mimic was eventually cured but Morph was enraged. He was devastated by Sunfire's death and told Mimic he should have killed himself rather than let something like this happen. Morph stormed off and threatened to leave the team. Magik, an unlikely ally, followed and tried to calm him. The two connected and despite her past attitude during missions, Morph realized Illyana was just a scared girl trying to get home. He remained angry with Mimic but helped his team fight against the rogue reality-hopping team, Weapon X.  Before the battle began, Magik attempted to switch sides, believing her team was weaker. Hyperion, the self-appointed leader of Weapon X, snapped her neck and Morph was driven into a rage. He attacked Hyperion, who attempted to blast Morph with his eyebeams, but Mimic saved him. During the brawl with Weapon X, Morph fought against an evil Ms. Marvel. Their battle caused a building to fall in on them, killing Ms. Marvel but Morph was able to survive.  The Exiles were triumphant and the Timebroker told Morph he could finally go home. His mission was fulfilled. Morph considered the offer but asked if he could stay with his team. He realized they needed him and he could not leave them behind. The Timebroker agreed; Morph asked him not to tell the rest of the Exiles of his decision. Morph and Mimic reconciled since he realized that Sunfire's death was not Mimic's fault and that the Brood was controlling him. The team moved on.  Morph helped the team take down Proteus by impersonating the Maestro and weakening Proteus with a steel strip in his head. Morph went to take down Proteus but Proteus knocked the steel plate out of his head and took over Morph's body in issue #80. When the Exiles tracked him to the "Heroes Reborn" world, cosmic entities "O" and "K" kidnapped him, saying his presence has tipped the balance of power. Using a tiara hooked to a brainwasher device, his teammate Blink managed if not to restore his consciousness, to brainwash Proteus, forcing him to act like Morph, and access to only Morph's memories, functionally "bringing him again to life." With Proteus trapped and believing he is Morph, he remained an Exile to continue fixing damaged realities. Considering Morph's body does not burn out like other hosts, Morph's consciousness is still active beneath Proteus. Also, Proteus is immune to metal while in Morph's body, since wearing a metal tiara during the "Heroes Reborn" world did not kill him. However, concerns about some discrepancies in "Morph's" behavior forced his teammates to plan regular brainwashings with the same device, and, eventually, put him in stasis whenever his behavior would change again. However, that device was destroyed when Psylocke and Sabretooth fought so intensely that they shook the Crystal Palace, causing a bookcase to fall on Morph's head, shattering the device. With the device shattered, it was only a matter of time before Proteus would re-emerge.  During a confrontation where Proteus reawakened, he found himself lacking in power to defeat the adversary. About to be crushed, Proteus shouted aloud his desire to stay alive. In a vision, he saw a figure, almost identical to his own true, energy form, telling him to take its hand, and he would survive. Upon doing so, Proteus found himself full of even greater power, using it to defeat his god-like enemy. Afterward, it was revealed that this being was the personality and soul of the true Morph, having been in limbo, gaining strength within Proteus and his own body, who had before only been able to speak a few sentences through Proteus' control. Revealing to Proteus that he had the ability to eject him from his body, Morph gave Proteus the chance to work together and share his body and their powers, in order to do more good, something which Morph had discovered Proteus desired deep within him. Proteus accepted, and the two now work together harmoniously, better than either could be alone.  However, soon after, when the New Exiles became immersed within the Crystal Palace, Proteus was absorbed in Morph's place, freeing Morph once and for all.

Q: what did Kevin Sydney have to do with Proteus?
A: weakening Proteus with a steel strip in his head.

Q: Is there any interesting information in the article?
A: Morph helped the team take down Proteus by impersonating the Maestro
How did he impersonate the Maestro?
unknown
unknown