Question: Who is the central protagonist of the long-running comic strip in which Snoopy remarks he is an "only dog"?

Context paragraphs:
Schroeder (Peanuts): Schroeder is a fictional character in the long-running comic strip "Peanuts", created by Charles M. Schulz.  He is distinguished by his precocious skill at playing the toy piano, as well as by his love of classical music and the composer Ludwig van Beethoven in particular.  Schroeder is also the catcher on Charlie Brown's baseball team, though he is always seen walking back to the mound with the baseball, never throwing it—admitting in one strip he did not want the other team to discover his lack of ability.  He is also the object of the unrequited infatuation of Lucy van Pelt, who constantly leans on Schroeder's piano, much to Schroeder's annoyance.  Charlie Brown, Frieda and Snoopy are also occasionally depicted as leaning on Schroeder's piano.

Snoopy vs. the Red Baron (video game): Snoopy vs. the Red Baron is a flight combat game released on the PlayStation 2, PlayStation Portable, and PC in 2006.  As the name implies, the protagonist is Snoopy, the dog in Charles M. Schulz's comic strip, "Peanuts".  The game is based on one of the most famous Snoopy alter egos: a World War I flying ace battling against Manfred von Richthofen, the Red Baron, the Flying Circus: Jagdgeschwader 1, the Austro-Hungarian Empire, and other enemies of the war.

Pee-Wee Harris: Walter "Pee-wee" Harris is a fictional Boy Scout who has appeared in several series of boy's books by Percy Keese Fitzhugh as well as in a long-running comic strip in the magazine "Boys' Life".  Originally spelled "Pee-wee", his name has occasionally been spelled "Pee-Wee" and is spelled "Pee Wee" in the "Boys' Life" comic strip.

Charlie Brown: Charlie Brown is the central protagonist of the long-running comic strip "Peanuts", syndicated in daily and Sunday newspapers in numerous countries all over the world.  Depicted as a "lovable loser," Charlie Brown is one of the great American archetypes and a popular and widely recognized cartoon character.

Ken Ernst: Kenneth Frederic Ernst (1918–1985), known professionally as Ken Ernst, was an US comic book and comic strip artist.  He is most notable for his work on the popular and long-running comic strip "Mary Worth" from 1942 to 1985.  With his realistic style, uncommon in those early years, Ernst paved the way for soap opera strips that followed.

Mark Alan Stamaty: Mark Alan Stamaty is an American cartoonist and children's writer and illustrator.  During the 1980s and 1990s, Stamaty's work appeared regularly in the "Village Voice".  He is the creator of the long-running comic strip "Washingtoon", as well as the earlier comic strip "MacDoodle Street", and the online strip "Doodlennium" for "Slate" magazine He is also a spot illustrator for "Slate".  He produced a monthly comic strip in the "New York Times Book Review" called "Boox" in 2001–2004 that made fun of publishing trends.

Snoopy's siblings: In Charles M. Schulz's comic strip "Peanuts", Snoopy was often stated to have seven siblings.  Five appeared at various times in the strip: four brothers, Andy, Marbles, Olaf, and Spike; and one sister, Belle.  The two others were never mentioned by name in the comic strip.  According to the 1991 TV special "Snoopy's Reunion", their names are Molly and Rover; however, their appearance is not considered canonical in the comic strip.  In the June 6, 1959 comic strip, following the birth of Charlie Brown's sister Sally, Snoopy remarks that he has no brothers or sisters, and is an "only dog."  However, in a March 18, 1971 strip, Snoopy writes in his autobiography: "I was born one bright Spring morning at the Daisy Hill Puppy Farm.  I was one of eight puppies."

J. Wellington Wimpy: J. Wellington Wimpy, generally referred to as Wimpy, is one of the characters in the long-running comic strip "Popeye", created by E. C. Segar in 1934 and originally called "Thimble Theatre", and in the "Popeye" cartoons based upon the strip.  Wimpy was one of the dominant characters in the newspaper strip, but when "Popeye" was adapted as an animated cartoon series by Fleischer Studios, Wimpy became a minor character; Dave Fleischer said that the character in the Segar strip was "too intellectual" to be used in film cartoons.  Wimpy did appear in Robert Altman's 1980 live-action musical film "Popeye," played by veteran character actor Paul Dooley.

Art Sansom: Arthur B. Sansom (September 16, 1920 – July 4, 1991), better known as Art Sansom, was an American comic strip cartoonist who created the long-running comic strip "The Born Loser".

Snoopy: Snoopy is Charlie Brown's pet beagle in the comic strip "Peanuts" by Charles M. Schulz.  He can also be found in all of the "Peanuts" movies and television specials, like "The Peanuts Movie".  Since his debut on October 4, 1950, Snoopy has become one of the most recognizable and iconic characters in the comic strip.  The original drawings of Snoopy were inspired by Spike, one of Schulz's childhood dogs.

Supporting paragraphs: Snoopy's siblings Charlie Brown
Answer: Charlie Brown