Shel Silverstein, the author of such acclaimed children's books as "A Light In The Attic" and "Where The Sidewalk Ends," was found dead of a heart attack. He was 66. Silverstein had severe coronary artery disease. Friends said he had recently complained of an upset stomach and "didn't feel quite right," said Dr. Richard Eicher, associate medical examiner. Two cleaning women discovered Silverstein's body in the bedroom of his home Monday. Eichler said he could have died Sunday or Monday. Silverstein's books, which he illustrated with his own humorous images, are packed with colorful characters like walruses with braces and camels in brassieres. His poetry is light and irreverent and humored children and adults alike. "It's a devastating loss," said his longtime friend and lawyer Sheldon Vidibor of Los Angeles. "I'm numb." Vidibor described him as "the sweetest brightest man that I know, good to everybody, loyal, loving. He's a wonderful person, a wonderful human being. It goes without saying, incredibly talented." The obituary goes on to mention some of his books but not the Uncle Shelby Coloring Book, some of his songs ("A Boy Named Sue," "One's On The Way" and "The Unicorn") but none of his work with Dr. Hook or The Smoke-Off or Freaking At The Freaker's Ball. Shel Silverstein began as a writer and cartoonist for Playboy magazine. He was an Oscar-nominated composer, creating popular country, pop and folk music. But it was his poetry collections and silly characters that thrilled children and brought him the most fame. The author of "A Light in the Attic" and "Where the Sidewalk Ends" was found dead in his apartment in Key West, where he had lived since 1978. He was 66. Two cleaning women discovered Silverstein's body in a bedroom of his home. An autopsy showed he died of a massive heart attack, possibly as early as Sunday. "It's a devastating loss. I'm numb," said longtime friend and lawyer Sheldon Vidibor. Vidibor described him as "the sweetest brightest man that I know, good to everybody, loyal, loving. He's a wonderful person, a wonderful human being. It goes without saying incredibly talented." Silverstein's self-illustrated books are packed with colorful characters like walruses with braces and camels in brassieres. His light, irreverent poetry entertained children and adults. But adults only were his first target. He began as a cartoonist for the Pacific Stars and Stripes while in the Army in Japan and Korea, and then wrote and drew cartoons for Playboy magazine in the 1950s. "Uncle Shelby's ABZ Book," published in Playboy in 1961, satirizes cloying children's books with such entries as "T is for TV," which urges readers to break open the television "and you will see all the cowboys and Yogi Bear and Shirley Temple and Huckleberry Hound and EVERYBODY! Wowee!!" The sardonic humor reappeared in Silverstein's music, which included "Cover of the Rolling Stone," recorded by Dr. Hook, and the Johnny Cash hit "A Boy Named Sue." The song tells of a man reunited in a bar with the father who named and then abandoned him. The resulting fight ends with the father explaining that he named his son Sue to make sure the boy grew up strong in his absence. "I got all choked up and I threw down my gun And I called him my pa, and he called me his son, And I come away with a different point of view. And I think about him, now and then, Every time I try and every time I win, And if I ever have a son, I think I'm gonna name him ... Bill or George! Anything but Sue! I still hate that name!" Silverstein's song "I'm Checkin' Out," written for the Meryl Streep film "Postcards from the Edge," was nominated for an Academy Award and a Golden Globe in 1991 as best original song in a motion picture. But his children's stories were arguably his most popular work. The books included "The Giving Tree" (1964), "Falling Up" (1996), "Where the Sidewalk Ends" (1974), "A Light in the Attic" (1981) and "The Missing Piece" (1976). "The Giving Tree" celebrates 35 years in publication this fall. Silverstein won numerous awards for his work, including the Michigan Young Readers Award for "Where the Sidewalk Ends." In the poem "Hug O' War" from "Where the Sidewalk Ends," Silverstein describes his favorite game: "I'd rather play at hug o' war, Where everyone hugs Instead of tugs, Where everyone giggles And rolls on the rug, Where everyone kisses, And everyone grins, And everyone cuddles, And everyone wins." "I would hope that people, no matter what age, would find something to identify with in my books, pick up one and experience a personal sense of discovery," Silverstein said told Publisher's Weekly in 1975. "That's great. But for them, not for me. I think that if you're a creative person, you should just go about your business, do your work and not care about how it's received." Survivors include his 15-year-old son, Mathew.