"Snoopy is the name of Charlie Brown's pet beagle in the long-running comic strip Peanuts, by Charles M. Schulz. Snoopy began his life in the strip as a fairly ordinary dog, but eventually evolved into perhaps the strip's most dynamic character - and among the most recognizable comic characters in the world. Animation producer Bill Melendez voiced both Snoopy and (eventually) Woodstock in numerous television specials from 1965 to 2003.

Snoopy first made his appearance on the strip on October 4, 1950, two days after the strip premiered, and was identified by name on November 10. Schulz was originally going to call him "Sniffy" (as described in 25th anniversary book, "Peanuts Jubilee", (pg. 20)), until he discovered that name was used in a different comic strip. Snoopy was a silent character for the first two years of his existence, but on May 27, 1952 he verbalized his thoughts to readers for the first time via a thought balloon; Schulz would utilize this device for nearly all of the character's appearances in the strip thereafter. In addition to Snoopy's ability to "speak" his thoughts to the reader, many of the human characters in Peanuts have the uncanny knack of reading his thoughts and responding to them. Curiously, the first time a beagle was mentioned, on December 5, 1960, Snoopy denied being one. As Snoopy dozed, Charlie Brown said, "Beagles on the grass, alas." To this, Snoopy replied, "I ain't no stupid beagle." Many of Peanuts' memorable moments come in Snoopy's daydream as a writer: his eternal opener on the typewriter "It was a dark and stormy night..." is taken from Edward George Bulwer-Lytton's 1830 novel Paul Clifford. The contrast between Snoopy's existence in a dream world and Charlie Brown's in the real world is central to the humour and philosophy of Peanuts (see e.g. Peanuts book title Life's a dream, Charlie Brown). Schulz summed up Snoopy's character in a 1997 interview: "He has to retreat into his fanciful world in order to survive. Otherwise, he leads kind of a dull, miserable life. I don't envy dogs the lives they have to live."

One of the first odd developments of Snoopy was his tendency to engage in impersonations. His earliest impersonation was of a bird on August 9, 1951. Later (starting November 17, 1955), Snoopy engaged in dead-on imitations of Violet, a pelican, Lucy, a moose, Beethoven and Mickey Mouse. He would also pretend to be various other animals, including a snake, rhinoceros, and vulture. But his eccentricities didn't stop there. On December 12, 1958, Snoopy slept on top of his doghouse, rather than inside it, for the first time. Subsequently, Snoopy started walking on two legs like a human. This soon became so commonplace as to be almost unnoticeable, as Snoopy developed a variety of alter egos, most notably the World War I flying ace. For this character he would don goggles and a scarf and fly his Sopwith Camel (actually his doghouse), battling the Red Baron. (The Red Baron, like other adult figures in Peanuts, was never drawn in a strip; his presence was indicated through the bulletholes that would riddle the doghouse in a dogfight, and Snoopy's angry outbursts in response: "Curse you, Red Baron!") Joe Cool as depicted over at the Universal Studios in Osaka, JapanSnoopy also became "Joe Cool," as he put on sunglasses and leaned against the wall doing nothing. He has also been a famous writer (who was actually published once, in an October 1995 storyline, in which one copy of his unnamed novel was written, but it failed to sell), an attorney (who once defended Peter Rabbit), a hockey player, an Olympic figure skater (who used to skate with Sonja Henie before he became "big time"), a world famous grocery checkout clerk who operated from the top of his dog house in an apron, the "Lone Beagle" (the first dog to fly solo across the Atlantic) and even the first astronaut to land on the moon. In one of the animated specials, Snoopy becomes a Flash dancer named "Flash Beagle". Outside of his fantasy life he is the shortstop for Charlie Brown's Little League team (and the best player, nearly breaking Babe Ruth's record of 714 career home runs before Hank Aaron). Snoopy is also a "Beagle Scout", the Peanuts version of Eagle Scout and is the Scout leader for a troop comprised of Woodstock and his other bird friends. This Scouting theme reappears throughout the comic strip. Snoopy loves root beer and cookies, hates coconut candy, gets claustrophobia, and is deathly afraid of icicles dangling over his doghouse. Snoopy also has the uncanny ablility to play fetch with soap bubbles, and can hear someone eating marshmallows or cookies at a distance (or even peeling a banana). He can also use his ears to fly about as a "whirlydog". Snoopy even became a canine helicopter, with Woodstock piloting. This gag appeared in the strip several times, most famously rescuing Linus from the top of a barn after being commissioned by Lucy. When asked by Linus where he learned to pilot, Woodstock replied in his usual apostrophes, which Linus interpreted as meaning "in Vietnam." Snoopy "understands a little French." His dog food brand is called "For Dogs who flew in World War I and understand a little French." He failed his high school geometry course, which was his excuse for not being able to follow a golf course's 90 degree golfcart driving rule. Snoopy has his own little dance, which was named by an outside observer, the "Snoopy Dance". Most often he dances at suppertime and has broken his foot being too excited. One strip includes a joke that he has forgotten the steps.

Over the course of the strip's run, it was revealed that Snoopy had been born and raised at the Daisy Hill Puppy Farm. His father used to run with hunting dogs, but would secretly run ahead and warn the rabbits. Snoopy's original owner was a little girl named Lila, who had to return him to Daisy Hill after her family moved to an apartment where dogs were forbidden. Shortly after his return to the farm, Snoopy was selected by Charlie Brown's parents as a companion for him. At one point in the series, Charlie Brown said that his parents bought Snoopy for him to cheer him up after another child threw sand in his face while they were playing in a sandbox. In the late 1970s Snoopy embarked upon a journey to visit Daisy Hill, only to find that the puppy farm had been replaced by a six-story parking garage. Snoopy is usually depicted as having seven siblings, five of whom appear at some point in the strip: Andy, Belle, Marbles, Olaf, and Spike. Most often seen is Spike, who lives in the desert (near the real-life locale of Needles, California) and is friends with cacti. Spike is very thin, wears a fedora and has long whiskers. Andy looks like a disheveled version of Snoopy. Olaf, who wears a fur cap, is rotund in both body and face. Marbles has spots on his fur, wears shoes, and considers some of Snoopy's behavior very odd. Belle, who looks like Snoopy with long eyelashes, is most notable in that there was a Belle stuffed animal available for many years. Although Snoopy often mentions that he was one of eight puppies, the two other siblings never appeared in the comic strip. According to animated special Snoopy's Reunion, they are named Molly and Rover. Many years before his siblings appeared, Snoopy referred to himself as an "only dog" who had no brothers or sisters.

Snoopy's best friend and confidante is the undersized yellow bird Woodstock, who only "speaks" in apostrophe marks. His arch-enemy (other than the Red Baron) is the unseen, vicious cat next door named "World War II". During one series of daily strips, Snoopy antagonized the cat each day, and the cat's paw made one giant slash move that, day by day, decimated Snoopy's freshly-rebuilt doghouse to a greater extent than the day before. In fact Snoopy reviled all cats generally, once remarking that they were "the crab grass on the lawn of life" and taking umbrage at the expression "cats and dogs", insisting that the proper expression was always "dogs and cats". Snoopy's owner is of course Charlie Brown, with whom Snoopy has a fairly indifferent relationship. (However, early in the strip he appeared to be a stray dog whom Charlie Brown and his friends had adopted - or vice versa.) The relationship between Charlie Brown and Snoopy was anything but master and servant. Charlie Brown's tormentor Lucy once demanded to know when he would be taking Snoopy to obedience classes; Snoopy wondered what would be the point, since Charlie Brown already did everything he (Snoopy) wanted. Snoopy almost never remembers his owner's name, usually referring to him as "that round-headed kid." His relationship with the other human characters is no more cordial than with Charlie Brown. Snoopy's deft and droll throwaway lines are an effective foil to Lucy's barbed remarks, making him less put-upon than the besieged Charlie Brown or the slightly hapless Linus. He often torments Linus by grabbing one end of the blanket, taking Linus for a soaring glide, twirling him and letting him go flying. On March 2, 1958, he declared himself the first dog to launch a human being. When Linus began to wear eyeglasses, Snoopy would abscond with them. For a while in 1977, Snoopy was engaged to an unseen female dog he met while on guard duty at Peppermint Patty's house. However, she ran off with Snoopy's brother Spike, and later a coyote upon their arrival at Spike's desert. This story was later adapted as the animated special Snoopy's Getting Married, Charlie Brown.

Snoopy's doghouse defied physics, being dramatically larger inside than it was outside, with several rooms. The first indication of the doghouse's unique layout occurred on January 31, 1954 when Charlie Brown was puzzled to see all his neighbourhood friends crawling into it for a visit. The interior was decorated with several pricey acquisitions including a Van Gogh, a fine kitchen (A Charlie Brown Thanksgiving), and sound equipment (A Boy Named Charlie Brown). The Van Gogh was later replaced by an Andrew Wyeth after his doghouse burned down and was rebuilt. The basement had a pool table, and there was even a reference to a TV at one point. Yet despite the wonders found in his doghouse, Snoopy was seldom seen to venture inside it, instead spending the bulk of his time sitting or lying on its pitched roof."