“Slapping a blot down as I begin stimulates the mind to guess and be inventive,” says Ralph Steadman of his creative method, showcased here in an exclusive excerpt of For No Good Reason. The Cheshire-born practitioner of wild illustration is best known for the feverish, ink-splattered imagery he created for the late American writer Hunter S. Thompson, most famously for his epoch-defining 1971 novel Fear and Loathing in Las Vegas. Over four decades later, this new documentary directed by Charlie Paul celebrates Steadman’s work, which ranges from books on Leonardo da Vinci, Sigmund Freud and birds, to commissions from Ted Hughes. “On paper, Ralph seemed violent and dangerous, yet in person he is one of the warmest and most generous people I have ever met,” says Paul. The 16-year labor of love is a raucous, whistle-stop trip through the archives, which have made him a hero to the likes of Johnny Depp, who narrates the feature. Depp’s involvement in the project stemmed from the actor’s long-standing friendship with the cartoonist after the pair crossed paths through Thompson. “Early on in the making of the film, I would come across pictures of Ralph and Johnny in Hunter’s home Owl Farm, so I knew they had a bond and a connection,” explains Paul. “Johnny instinctively knew what to ask Ralph about. A chemistry existed between them, making it a natural dynamic to film.”

For No Good Reason is available on DVD and On Demand now.