In his long career, Ray Bradbury was an inspiration to many science fiction readers, often beginning in their youth, and to many science fiction creators. Neil Gaiman praised him as "an author who made me dream, taught me about words and what they could accomplish, and who never let me down as a reader or as a person as I grew up."
Steven Spielberg observed,"he was my muse for the better part of my sci-fi career." Bradbury influenced writers as various as Margaret Atwood and Michael Chabon.
As others agreed (including scores of comments on various tribute threads), Bradbury was important to people personally as well as for his writing. As Gaiman wrote, "he was kind, and gentle, with that midwestern niceness that's a positive thing rather than an absence of character. He was enthusiastic, and it seemed that that enthusiasm would keep him going forever. He genuinely liked people. He left the world a better place, and left better places in it: the red sands and canals of Mars, the midwestern Halloweens and small towns and dark carnivals."
Bradbury also had a specific relationship to Star Trek, and especially to Gene Roddenberry. As he said in his remarks at Roddenberry's memorial services (published as his Foreword to David Alexander's biography of Roddenberry), the two were often mistaken for each other. He praised Star Trek for exploring the miracles of life and death, and for being "a moral example in a time when we need it," "in the midst of so much violence and so many shows we don't care about."
Bradbury ended his remarks with part of one of his own short stories, about his great-grandmother who died at an advanced age. In the story she said that "A long time back...I dreamed a dream, and was enjoying it so much, when someone wakened me, and that was the day I was born." As she lay dying she was seeing the shape of that dream return. "It's all right, whispered great-grandma, as the dream floated her. Like everything else in this life, it's fitting. And the sea moved her back down the shore."
Ray Bradbury, who dreamed awake better than almost anyone, died at the age of 91.
Here's a short New York Times essay on Bradbury's place in literature, for both his sources and his own writing transcended any genre. And here's Wired's series of Bradbury videos (talking about writing as well as his own works) and tributes, including a tweet from LeVar Burton.