Marvel Comics Editors in Chief

Joe Simon (1940-1941): Co-Creator of Captain America, and one of Marvel's earliest resident talents.
Stan Lee (1941-1942, 1945-1972): Certainly the most famous in comics, and even those who think Jack Kirby and Steve Ditko did most of the hard work will attribute him as the most important editorial hand in the history of comics.
Vincent Fargo (1942-1945): Handled the company while Lee was doing service in WWII. His main impact was a large amount of Funny Animal titles.
Roy Thomas (1972-1974): A natural choice to follow in Lee's footsteps, as the first Promoted Fanboy at the company, and was the writer with the largest pull after Lee.
Len Wein (1974-1975): Was editor for the briefest of the times, but he did make his mark by reviving a little book called X-Men...
Marv Wolfman (1975-1976)
Gerry Conway (1976)
Archie Goodwin (1976-1978): Would later mark his mark handling Marvel's epic line.
Jim Shooter (1978-1987): One of the longest lasting, and most controversial editors. Helped electrify the company after sagging sales, and spearheaded many beloved runs, but his tenure came to an end amidst micro-managing the talent, and conflicts with the powers that be.
Tom Defalco (1987-1994): Succeeded Shooter, and was on board during the comics boom of the late eighties and early nineties. Interestingly, despite presiding over a period that was considered speculation-heavy and crass, he manages to deflect a lot ire the industry pumps like oil. This is probably largely due to his laid-back persona, his quietly going back to writing, (including the fan-favorite Spider Girl) and Ron Perelman nicely positioning himself as the Big Bad of the era.

In 1995, the decision was made to split the editor-in-chief position five ways. This only lasted a year, as Marvel's line shrank drastically.

Bob Harras (1996-2000): Gained prominence by more or less running the X-Men line, so that when the editor-in-chief position was consolidated again, he was pegged as the natural choice. Word is, he made his enemies around the office, and some were not pleased at his resolution of the Spider Clone saga (though to be fair, it was an inherited mess), but what may have ended his tenure was the inability for the X-Men comics to resemble, let alone capitalize, on the upcoming film. Although a great deal of titles were bland, directionless, or even experiencing a Dork Age through his stewardship, a few of his efforts were positive as well. The majority of the non-mutant characters were reinvigorated and finally given top-notch creative talents. Deadpool was tested out with his own book, and has become the Breakout Character of the nineties. Harras also greenlit the Thunderbolts, a property that still sticks around here and there.
Joe Quesada (2000-2011): Currently Editor-in-Chief of Marvel Entertainment (which includes not only comic publishing, but video games, films, etc.), and the second longest-serving EIC of Marvel Comics. Started out as controversial, but got some good notice for cleaning house at the company. However, is now controversial for storylines like One More Day.
Axel Alonso (2011-2017): Once Editor-in-Chief of Marvel Comics. Alonso's appointment was a brief moment of And the Fandom Rejoiced for Quesada's critics, but it was quickly clarified that Quesada was being promoted to an even higher position of creative control, not fired. Alonso quickly proved unpopular for a very political, anti-fan shift (among other problems) which when finally reached the attention of the higher ups got him fired.
C. B. Cebulski (2017-present): Current Editor-in-Chief. While unknown to the general public before his appointment he was a writer for the Marvel Mangaverse and an editor. Simultaneously held writer and editor position at Marvel, despite not being allowed by Marvel's internal rules at the time, as a result of Marvel separately hiring his alias (an intentionally and clearly fake name) and him not disclosing it because it was short term, freelance work. His alias did well enough to get a follow up offer and he, in true comic book fashion, played it through by having his friend pretend to be him for a meeting. Made his entry felt by swiftly canceling several poorly selling books only kept running by playing to Alonso's politics (as well as Gwenpool).