Ascended Fanon: Catbert was initially just someone who tried to eat Ratbert. Adams then started getting fanmail for more 'Catbert'. He never actually named the cat; still, given the response and how his use of Theme Naming could lead to this, he kept the cat and gave him a perfect job. His reasoning being that if your entire fanbase spontaneously and unanimously names a character for you, you should probably keep him.
Many fans commented on a resemblance between The Pointy Headed Boss and Phil, Prince of Insufficient Light. Scott Adams claimed that this was just because he wasn't that good at drawing different faces but decided to introduce a plot line where it was revealed that they were brothers.
Fan reaction generally seems responsible for determining which one-shot characters become regulars (Catbert, Ratbert, Topper) and which don't (Camping Carl, Single Task Bob, Sourpuss).
Executive Meddling: A beneficial instance was when Adams wanted to feature Satan in the comic and the editor said no. Thus was borne Phil the Prince of Insufficient Light which Adams admits is a funnier concept.
Less benign example: while the Cubicle Gestapo is an inherently funny concept, the minefield of figuring out how many Nazi references a newspaper comic can get away with makes their appearances more trouble than they're worth.
Name's the Same: The title character was inadvertently named after a comic character from The Forties who would feature in US Air Force publications as a humorous example of 'How Not To Do It'. Adams asked for name suggestions from his friends, and the winner didn't realize he must have recalled the name from the earlier comic until after Dilbert had already become famous.
Write What You Know: Dilbert started running while Adams was still working at Pacific Bell, with Wally being mostly a non-speaking background character. Then the company began offering buyout packages to the employees, with the caveat that they were only available to the lowest 10 percent of the workforce(as a way to get rid of deadweight). One of Adams' coworkers(who Adams describes as "one of the more brilliant people I've ever known") decided that was a fine idea and began to "work as hard as he could to become the worst possible employee in order to get money for leaving", which included openly running a side business from his cubicle. Adams loved the concept of a cynical employee with no loyalty to his employer, and Wally was born.
Write Who You Know: Adams has said that Wally, Alice, Carol and Asok are all based (with varying degrees of precision) on ex-coworkers from Pacific Bell.
Hey, It's That Voice!: Several of the voice actors are well-established, as are some who aren't commonly known for voice acting but can still be easily recognized from their many live-action roles (Kathy Griffin, the voice of Alice, is uncredited for some reason), but the Garbage Man is voiced by Maurice LaMarche, who is in many, many animated works and games and can be recognized from the Garbage Man's voice as such varied characters as The Brain, Kif Kroker and Morbo, and Abraham Lincoln.
Screwed by the Network: Despite the show's high ratings (by UPN's standards), the show was canceled due to the network's decision to focus entirely on minority groups (primarily African-Americans) in the station's line-up, notably the show that aired right before Dilbert, Shasta McNasty. The fact that UPN went off the air shortly afterward shows how good an ideathat was.
For its second season, the series had also been moved from its fairly successful Monday night timeslot to Thursdays - up against NBC's then-quite powerful lineup.