Besides being one of the most important figures in 20th-century science fiction, this guy was nuts. 

Also one of my favourite writers.

Dick exemplified the cliché about there being a fine line between genius and madness. He was known for ingesting huge amounts of drugs to keep himself writing without sleep for weeks at a time to complete his novels and short stories, and toward the end he was clinically schizophrenic. And yet that's when his most intriguing works were composed.

Born in Chicago, he began his writing career in the early 1950s. Almost from the beginning, his works dealt with alternative realities with his characters often crossing over into other worlds. Time is twisted out of joint, human and machine are melded, reality and illusion are mixed, virtual realities are embedded in virtual realities, until the reader—and, one suspects, the author—can no longer keep it all straight. But that's all right, for Dick's point is often that no reality is more real than any other. During the last decade of his relatively short life, Dick became certifiably insane. But his paranoia continued to provide material for his work.

His writing often seems slapdash. His characters generally have no fixed personalities. And elements of his plots are often built up only to be forgotten as the narratives take different turns. But, for the reader who is willing to sit back and enjoy whatever may occur, Dick always makes for compelling reading.

Here's part of what the Grolier Multimedia Encyclopedia of Science Fiction says about Philip Kindred Dick:

The earlier PKD often lost control of his material in ideative mazes and, sidetracked, was unable to find any resolution; but, when he found the tale within his grasp, he was brilliantly inventive, gaining access to imaginative realms which no other writer of sf had reached. His sympathy for the plight of his characters—often far-from-heroic, small, ordinary people trapped in difficult existential circumstances—was unfailing, and his work had a human interest absent from that of writers engaged by complexity and convolution for their own sake. Even the most perilous metaphysical terrors of his finest novels wore a complaining, vulnerable, human face. In all his work he was astonishingly intimate, self-exposed, and very dangerous. He was the funniest sf writer of his time, and perhaps the most terrifying. His dreads were our own, spoken as we could not have spoken them.

The most recent Dick work to be adapted, as of this writing, is his paranoiac novel A Scanner Darkly (1977), made into a semi-animated (interpolative rotoscoping, I think they call it) film by Richard Linklater in 2006, starring Keanu Reeves, Robert Downey Jr., Winona Ryder and Woody Harrelson. It's the most authentically Dick flick ever, with huge patches of his insane, but so real, dialogue lifted from the book.