Gilbert Shelton, creator of The Fabulous Furry Freak Brothers, a series of satirical counterculture comics that have been published in 15 languages and racked up worldwide sales of over 40 million copies, turns 75 on May 31, 2015.

To celebrate the birthday of one of the most influential comic artists of the past 40 years, Sequential, the digital graphic novel app for iPad, has partnered with Freak Brothers UK publisher, Knockabout Comics, to release The Sequential Guide to Gilbert Shelton’s Fabulous Furry Freak Brothers. The digital collection, which is almost 100 pages long, is available to download free, exclusively on the Sequential iPad app, until the end of June 2015.

Containing the complete Underground Classics #1, the visual history of the Freak Brothers as written by Gilbert Shelton and a plethora of rare comic strips, illustrations and photographs, this massive free collection is the perfect way to reflect on the achievements of the great American comix pioneer.

Along with Robert Crumb, Gilbert Shelton is considered to be one of the founders of the underground comix culture of the late 1960s and early 1960s, epitomised in the anti-establishment slapstick and satire of the Freak Brothers.

Shelton was drafted for the Vietnam War in 1964 but declared medically unfit after admitting to taking LSD. 1969 saw the first appearance of Freak Brothers spin-off comic strip, Fat Freddy’s Cat, in the same year that Shelton founded Rip-Off Press. In 1978 he created the cover art for The Grateful Dead’s Shakedown Street and Shelton was inducted into the prestigious Eisner Award Hall of Fame in 2012.

The Sequential Guide to Gilbert Shelton’s Fabulous Furry Freak Brothers is downloadable for free from the Sequential iPad app, which is available for free on iTunes here.