The Dude is actually based on a real person
Jeff Bridges’ performance of the Dude character has a sort of general “Hey, I know a guy just like that!” resonance, but believe it or not, he was based on a real person. They’re not even subtle about it in the film, listing actual autobiographical details of Jeff Dowd, the man the character was based on, in an afterglow scene where Lebowski and Maude talk post-coitus.
Jeff Dowd really was one of the “Seattle Seven,” an actual anti-war activist group during the ’60s, and The Port Huron Statement was a real document authored by the group. The Metallica “Speed Of Sound” tour is fictional, however, and Dowd had no connection to that group at the time of the film. In a strange twist of fate, however, he did end up working on Metallica’s documentary film Monster, and we’ll leave it up to you to decide whether that plot twist was fortunate or not.
In real life, after his protest activism slowed down, Dowd was very active in the film industry as a producer and filmmaker, very unlike the slacker image presented in the film. Among his other work, he was the co-producer of FernGully: The Last Rainforest and… wait, what? FernGully? Really? Wild.