Comic book pioneer and media mogul Stan Lee died at the age of 95 on Monday morning. Lee spent much of his teenage years living in University Heights and attending DeWitt Clinton High School in Bedford Park. Cause of death is not known.

One of the most prolific contributors to the American superhero pantheon, Lee remained active his entire life, executive producing and making cameo appearances in every Marvel Cinematic Universe film. Less than a week before his death, Lee’s official Twitter account tweeted out a class photo from his time at DeWitt Clinton High School in the 1930s.

Lee is one of many notable alumni from DeWitt Clinton High School, including comic book pioneer Will Eisner and Batman co-creator Bob Kane, who both attended DeWitt Clinton a few years before Lee.

I spy with my little eye someone who looks like teenage Stan Lee in this 1930s picture taken at DeWitt Clinton High School in the Bronx. #MondayMotivation #MondayMorning pic.twitter.com/Uj0lgislgP

— stan lee (@TheRealStanLee) November 5, 2018

Born Stanley Lieber in Manhattan’s Upper West Side in 1922, Lee’s family moved around the city several times before settling in the Bronx during his teenage years. While attending DeWitt Clinton High School, Lee lived on the third floor of a still-standing apartment building on 1720 University Ave.

In 1939, Lee graduated from high school a year early, at age 16, and began working for Timely Comics, a predecessor of Marvel Comics. By 1941, he was playing a role in the production of Captain America comics and, at age 19, was named editor-in-chief and art director of Timely Comics.

When America entered World War II in early 1942, Lee joined the Army and worked in the Signal Corps for a time repairing telegraph poles in New Jersey. He was eventually transferred to the Training Film Division in Astoria, Queens, where he would make training and propaganda materials through the end of the war in 1945.

Returning to comic books postwar, Lee worked with artists like Jack Kirby and Steve Ditko to create beloved Marvel characters like the Hulk, Thor, Iron Man, Spider-Man, Daredevil, Doctor Strange, and Black Panther. Lee’s career also produced the X-Men, the Fantastic Four, and the Avengers. By the 1970s, Lee was a star in his own right and the public face of Marvel. Through the course of his career, Lee would serve as publisher, president, chairman, editor-in-chief and, finally, chairman-emeritus of Marvel Comics. Lee was also known by signing off his letters with, “Excelsior!”

In recent years, Lee stayed active, posting videos online and appearing at public events, but internal conflict involving his family and estate became public following the death of his wife Joan, 95, in July 2017. The couple had been married for almost 70 years. Battles over Lee’s estate, estimated to be worth around $50 million, produced accusations of elder abuse against his 68 year old daughter (which Lee dismissed in interviews) and the arrest of his longtime road manager.

Lee is survived by his daughter, JC Lee.