Doug was part of the first wave of Nickelodeon's "Nicktoons" line of in-house animated series, along with Rugrats & The Ren & Stimpy Show. Network executives thought Doug, about an average Everykid, would be the breakout hit of the three, but it wasn't (Rugrats was).
Doug Funnie (voiced by Billy West) appears to be a normal, average kid. He has a pet dog, Porkchop, who is his best friend, and he pines for the love of one of the most popular girls in town, Patti Mayonnaise. Doug, though, is also a dreamer, and his Walter Mitty-esque fantasies recast him as a secret agent, a cowboy, or a superhero, depending on the plot of a particular episode.
Doug was in production for just 3 seasons on Nick before creator-producer Jim Jinkins sold his production company, Jumbo Pictures, to Disney, which revived Doug in 1996 and moved him to ABC as part of their One Saturday Morning block. There, Doug lasted another three seasons, and even got a feature film out of the deal. By then, Tom McHugh took over as the voice of Doug, who was no longer alone in pretending to be a superhero; Patti and Skeeter Valentine also adopted heroic alter egos during the Disney series.
Unfortunately, reruns of either incarnation of the series are not to be found either on Nick or Disney Channel these days. For now, here's the open to the 1996 Disney reboot:
Edit: 3/12/14: The open to the original Nickelodeon series has been deleted due to copyright concerns.