He later worked as an editor at DC Comics from 1994 to 2000, during which he edited a number of books published under their Vertigo line, such as Doom Patrol, Animal Man, Hellblazer, Preacher, and 100 Bullets.

One day, he saw an ad in The New York Times for DC Comics editors and thought it would be fun to interview, never thinking he would actually be offered a job, though he ended up being hired by the publisher.

Other Vertigo titles he edited until 1999 included Garth Ennis' Preacher, Black Orchid, Kid Eternity, Hellblazer, Unknown Soldier, 100 Bullets, and Human Target.

[12] Alonso is also credited with bringing crime writers to work on Marvel titles including Duane Swierczynski and Victor Gischler.

[13] Alonso edited stories featuring the Western character Rawhide Kid,[10] the first of which was the 2003 biweekly Marvel Max miniseries Rawhide: Slap Leather by Ron Zimmerman and John Severin, which drew controversy[14] for its depiction of the titular character as a homosexual, albeit through the use of innuendo in the book's design and dialogue.

[10] He was promoted to vice president, executive editor in early 2010, and oversaw cross-promotional projects such an issue of the ESPN The Magazine, which depicted several NBA basketball players as Marvel superheroes.

[22] In May 2016 a storyline that saw Captain America transformed by timeline manipulation into a double agent for the evil, Nazi-like organization Hydra[23] prompted such criticism that Marvel released a statement indicating to readers the character would eventually be reverted to his original benevolent, patriotic identity,[24] which occurred in August 2017.

[25] In April 2017 Marvel was subject to substantial criticism on social media after statements made by Vice President of Sales David Gabriel in an interview with ICv2 were understood to mean that retailers attributed poor sales of Marvel books to the company's effort to promote diversity with prominent non-white and non-male characters in starring roles in its books.

The publisher announced that its first slate of titles would include books by creators such as Peter Milligan, Frank Cho, and Christa Faust.

The series, which was intended to establish a new superhero universe, debuted on March 18, 2020,[30][31] as the COVID-19 pandemic was taking hold in the United States.