According to Mountain Girl, Garcia originally purchased the hat in a costume shop in San Francisco in 1966: Stars and stripes, and red white and blue were popular themes in new art during the rebellious 1960's as American youth sought to expand their civil liberties by wearing flag-themed clothing and to attract attention and to identify changing behaviors in America as freedoms [were] protected by the U.S. Constitution... [He] wore it to public appearances, concerts with the band, and in photos by well-known San Francisco photographer Gene Anthony, who documented the ‘Summer of Love’ in Haight-Ashbury.
Garcia chose to wear the hat for the now famous shoots with Gene Anthony on the steps of the Grateful Dead communal house at 710 Asbury and with Herb Greene at the home of Gene Estribou, who recorded one of the first demos for the band. Photographs from both shoots were used for the cover and liner of the Grateful Dead’s 1967 debut album The Grateful Dead, where the corresponding liner notes named Garcia as Jerry ("Captain Trips") Garcia. The hat became synonymous with Garcia’s ‘Captain Trips’ persona. Herb Greene remembers …Garcia became Captain Trips when he put it on.
According to Denise Kaufman of The Ace of Cups, the nickname originally came from an episode at Ken Kesey's Acid Test at the Big Beat Club, Mountain View in Palo Alto on 18th December, 1965: At one point, I was standing out in the parking lot talking to Jerry Garcia, and this police car drove up… It was the usual: "What's going on here?" Whatever Jerry said satisfied him because he turned to leave. As he turned to walk away, Jerry kind of tipped his hat and said, "The tips, captain." The way he said it just knocked me out. I told Kesey about this interaction and out of that Jerry got his name Captain Trips. Of course, the nickname also reflected Garcia’s fondness for psychedelic drugs and his prototypical psychedelic persona, although he came to dislike the moniker himself.
According to Mountain Girl, The hat was part of Jerry Garcia's personal wardrobe for several years and when he stopped wearing it, he gave it to his friend Harry Tsvi Strauch who ran a gallery on Haight Street. Strauch explains …In the Summer of 1966, The Grateful Dead became our neighbors, moving into 710 Ashbury, the house two doors up from ours. September 1967, an anti-War/Peace march was to come through Haight Street for a rally at Kezar Stadium. My wife - Hyla Strauch - was designing a Red, White & Blue American Flag themed window display for our shop in support of the march. She thought that Jerry Garcia's Capt'n Trips hat would be the ideal, iconic centerpiece for the display. We brought this up to Jerry, and he gave us the hat to use in the shop window! When it was time to take the display down, we offered to return the hat - Jerry Told us "I don't want the hat...You keep it, take care of it."