Spiff is one of Calvin's many alter egos, imaginary personae who have solo adventures (without Hobbes's company) in fantasy worlds which usually have some form of indirect connection with his home or school life. He travels through the galaxy in a red flying saucer with a bubble canopy. In all but one strip, the saucer is tiny, with just enough room for Spiff and apparently little else. Yet, the craft is equipped with an astounding array of weapons, detectors and propulsion devices. Spiff wears square glasses, or goggles, whose front openings change their shape according to his emotions. The galaxy is a cruel place where Spiff is often zapped by ferocious and disgusting aliens (who, in reality, are really people such as Calvin's parents, Miss Wormwood, etc.) or stranded on a desert planet or both. He has a raygun, known by various fantastic names, but in reality, it is merely a water pistol.
The Calvin and Hobbes Tenth Anniversary Book provides background on Spiff's character. Watterson first conceived an earlier version of Spiff when he was taking a high school German class, producing a two-page comic titled "Raumfahrer Rolf". When he was in college he reworked the strip and renamed his hero "Spaceman Mort". Later on, after finishing college, he came up with the name Spaceman Spiff and made what he hoped was a professional strip with Spiff as a hero. There was little resemblance to the Calvin-Spiff character: The early Spiff was a "diminutive loudmouth" with a Chaplin moustache who explored space in a dirigible with his sidekick Fargle. The newspaper syndicates all rejected this early strip, and the present Spiff was finally born as one of the many imaginary alter egos of Calvin when the Calvin and Hobbes strip took off.
Early in the strip's career, the alien planets Watterson invented were, in his words, "rather generic". As his work matured, Watterson brought the Spiff saga in line with his principle that "Things are funner when they're specific, rather than generalized", basing his alien landscapes on the rock formations of southern Utah, as well as the landscapes within Krazy Kat. Gradually, the monsters also took on more detail, becoming more than blobs of slime. The vocabulary, and in particular Spiff's array of high-tech gadgetry, offered a caricature of the "Science" found in many science fiction books and TV series.
Watterson himself described Spaceman Spiff as a parody of Flash Gordon. The grand "space opera" style of Spiff's adventures may also point to a spoof of Star Trek and Star Wars; there is very little cyberpunk in Watterson's oeuvre. Since all the Spiff adventures have a lone protagonist playing with reality, they resemble the early work of Philip K. Dick and that of other writers who featured lone individuals going to the edge of their perceived world.
In the final years of Calvin and Hobbes, Watterson began to show an interest in information technology, often pitting the progressive and computer-savvy Calvin against his reactionary father, who comments, "It's bad enough to have a telephone." Watterson's satire of the personal computer and its effects spilled over into the Spaceman Spiff strips.
Calvin had many other science fiction adventures, in addition to the Spiff episodes. Some of them delved farther than the Spiff stories in exploring the aesthetics of science fiction and the nature of id and otherness.