Snoopy pretending to be a vulture.
The Fierce Vulture is one of Snoopy's many alter egos.
Snoopy first adopted this alter ego in the strip from May 13, 1958. Despite the Beagle's adopting many different animal alter egos in the early years of Peanuts, the Vulture was the only one that was stabilized into appearing throughout the whole strip's history.
The strip from May 13, 1958, the first appearance of The Fierce Vulture.
When Snoopy is pretending to be a vulture, he often perches on some sort of object, most frequently a small tree that the other characters can reach the top of, or a snowman. He then sits in wait for a "victim," most often being Linus or Frieda. However, his attempts to attack a victim always fail through a variety of reasons, from Linus tricking him to Frieda calling him "Sweetie," a name that vultures supposedly hate to be called.
The strip from July 18, 1967.
Other characters have mixed feeling of the Fierce Vulture. Lucy commonly voices her protests against the vulture, in one strip stating that "Anybody who would sit on a tree pretending to be a vulture should go to see a psychiatrist." Charlie Brown never does much to stop Snoopy's actions, but does show disapproval to the game. Frieda and Violet both take a passive approach to blocking an attack, commonly complimenting him before he has the chance to swoop down on them or revealing a truth about vultures that prevented Snoopy from going further. Linus' opinions vary, sometimes being terrified of the vulture and retreating to the house, but other times he goes against his attacker, whether it be tickling him out of the tree, ruining Snoopy's mood to play, or revealing a vulture fact that ends the game.