Question: The Fearsome Foursome is a fictional supervillain group, appearing in American comic books, it included which  fictional character, a supervillain appearing in American comic books published by Marvel Comics? 

Context articles: Amazo
Massacre (Marvel Comics)
Namor
Isbisa
Cyber (comics)
Klaw (Marvel Comics)
Bloodshed (comics)
Fearsome Foursome (comics)
Leader (comics)
Ultron

Amazo is a fictional supervillain appearing in American comic books published by DC Comics.
 The character first appeared in "The Brave and the Bold" #30 (June 1960) and was created by Gardner Fox and Murphy Anderson.
 Debuting in the Silver Age of Comic Books, the character has appeared in comic books and other DC Comics-related products, including animated television series, trading cards and video games.
Massacre is a fictional supervillain appearing in American comic books published by Marvel Comics.
 He primarily appears in Spider-Man related publications.
 The character is responsible for the murder of Ashley Kafka, a supporting character in various Spider-Man comic books and adapted media.
Namor the Sub-Mariner ( ) (Namor McKenzie) is a fictional character appearing in American comic books published by Marvel Comics.
 Debuting in early 1939, the character was created by writer-artist Bill Everett for Funnies Inc., one of the first "packagers" in the early days of comic books that supplied comics on demand to publishers looking to enter the new medium.
 Initially created for the unreleased comic "Motion Picture Funnies Weekly", the Sub-Mariner first appeared publicly in "Marvel Comics" #1 (cover-dated Oct. 1939) – the first comic book from Timely Comics, the 1930s–1940s predecessor of the company Marvel Comics.
 During that period, known to historians and fans as the Golden Age of Comic Books, the Sub-Mariner was one of Timely's top three characters, along with Captain America and the original Human Torch.
 Everett said the character's name was inspired by Samuel Taylor Coleridge's poem, "The Rime of the Ancient Mariner".
 Everett came up with "Namor" by writing down noble sounding names backwards and thought Roman/Namor looked the best.
Isbisa is a fictional supervillain appearing in American comic books published by Marvel Comics.
 He first appeared in "All Winners Comics" vol.
 1, #19 (Fall 1946), published by Marvel predecessor Timely Comics during the 1940s period fans and historians call the Golden Age of Comic Books.
 He was created by writer Bill Finger and one or more of the five artists who contributed one or more chapters to his 44-page debut story.
Cyber is a fictional supervillain appearing in American comic books published by Marvel Comics.
 The character is depicted usually as an enemy of Wolverine of the X-Men.
 Created by writer Peter David and artist Sam Kieth, he first appeared in "Marvel Comics Presents" #85 (September 1991), though his appearance was obscured by a trench coat and hat.
 He was first fully seen and named in "Marvel Comics Presents" #86 (September 1991).
Klaw (Ulysses Klaue) is a fictional character, a supervillain appearing in American comic books published by Marvel Comics.
 He is depicted as a human physicist who has been transformed into solid sound, and who wears a sonic emitter on his right wrist as a prosthetic device.
 He has often been shown in conflict with the Fantastic Four and the Avengers and is an enemy of the Black Panther and Ka-Zar.
Bloodshed (real name Wyndell Dichinson) is a fictional supervillain appearing in American comic books published by Marvel Comics.
 It is also the name of a supervillain in Marvel's Razorline imprint, as well as a character in comics from an acquired company, Malibu Comics.
The Fearsome Foursome is a fictional supervillain group appearing in American comic books published by Marvel Comics.
 It was made up of Devos the Devastator, Huntara, Klaw, and Paibok the Power-Skrull.
 They worked together to destroy the Fantastic Four, though they also came into conflict with the Avengers.
The Leader (Samuel Sterns) is a fictional character, a supervillain appearing in American comic books published by Marvel Comics.
 The Leader first appeared in "Tales to Astonish" #62, created by writer Stan Lee and artist Steve Ditko as an enemy of the Hulk.
 He has mainly appeared in Hulk related comic books over the years and was one of the featured characters in the Marvel NOW!
 Thunderbolts relaunch.
 In 2009, The Leader was ranked as IGN's 63rd Greatest Comic Book Villain of All Time.
Ultron ( ) is a fictional supervillain appearing in American comic books published by Marvel Comics.
 He is most recognized as a nemesis of the Avengers, and has a quasi-familial relationship with his creator Hank Pym.
 He was the first Marvel Comics character to wield the fictional metal alloy adamantium.