The Waldos invented 420
A group of kids known as the 'Waldos' invented 4:20 as a term to mean smoking cannabis.
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The date 4/20 is associated with modern marijuana culture. It is a widely celebrated, unofficial holiday. The origins of 4/20 as a term and holiday related to marijuana have never been definitively figured out. Doing so would put a decades-old cultural debate to rest.
Around 1971, five teenaged boys met at a wall, hence the nickname “Waldos.” There, they smoked marijuana at approximately 4:20pm, directly after school and its activities. They began referring to hanging out to smoke as “420,” and so the term was born.  Since then, it has become both slang for hanging out to smoke marijuana, and also for the holiday that celebrates marijuana occurring April 20th. Through a connection between one of the original five teenagers and a member of the Grateful Dead, the term gained notoriety and is now part of American popular culture. The original five teenagers who purport this theory are still alive and continue telling their part in it from their homes in California. 
The only people around to verify that “The Waldos” are the ones who started 420 are The Waldos themselves. They could have grabbed hold of this mystery in an effort to gain media attention or personal acclaim. There is no outside proof that this argument is anything other than fiction, so we cannot argue that it is the holiday's origin story.