How did marijuana become associated with 4/20?

April 20, or 4/20, is pretty much known as the stoner’s Christmas. Yet it has been associated with many things, including Adolf Hitler’s birthday and, incorrectly, the number of chemicals in cannabis.

TIME that he and his friends would meet outside of San Rafael High School at 4:20 p.m. by the statue of chemist Louis Pasteur to smoke up. The group, which called themselves the “Waldos” because they met at a wall after school, used the code word “420” when talking about marijuana.

“We got tired of the Friday-night football scene with all of the jocks. We were the guys sitting under the stands smoking a doobie, wondering what we were doing there,” Reddix previously told TIME.

The code word really caught on thanks to the Grateful Dead, with whom the Waldos had some connections. One of the friend’s brothers was the manager for Dead bassist Phil Lesh’s side project; another friend’s dad bought real estate for the Bay Area-based band.

Fast forward 20 years and High Times magazine published a Grateful Dead flyer that explained the famous code.

"There's something magical about getting ripped at 4:20, when you know your brothers and sisters all over the country and even the planet are lighting up and toking up right along with you," the flyer read.

In 2013, 420 Magazine reported that another group of friends from San Rafael, California claimed to have coined the term. The Waldos defended their claim in a Huffington Post article—with evidence.

“We're the only ones with evidence," said Steve Capper, one of the Waldos. In the article, Capper and Reddix said all evidence of the origins of 4/20 is "preserved in a bank vault, have been examined by legitimate respectable journalists, and continue to be available for inspection by official Press."

No matter where the term came from, marijuana advocates say that the best way to celebrate the stoner holiday is to legalize and decriminalize marijuana. Erik Altieri, executive director at NORML, an organization that works to reform marijuana laws, said in a statement to Newsweek that marijuana consumers should take action to get marijuana legalized in the U.S.

“On this holiday, marijuana consumers and legalization supporters should take action to contact their elected officials at both the state and federal level and demand an end to our failed experiment with prohibition,” Altieri wrote.