In an interview, Nathan Fillion said that when Joss Whedon called to offer him the part of Captain Hammer, Fillion saw Whedon's name on his caller ID, immediately picked up the phone, and said "Yes!" Whatever Whedon was calling to talk to him about, his answer was going to be yes.
"Dr. Horrible's Sing-Along Blog" garnered the first-ever Emmy win for Joss Whedon, despite both his long and critically acclaimed career as a writer, director, and producer of many television shows and the fact that it did not actually air on television.
On the DVD, the ELE warning that flashes on the screen during the FBI warning reads "This video disc is designated for Evil purposes only, and any and all non-evil use will result in immediate self-hatred. Evil Rule of Evil #24B states that any and all infringements constitute an Extreme Offense with the maximum penalty of up to five nails driven into the offending skull and a $250,000 fire. DON'T BE A HERO!"
Dr. Horrible's evil lair is a real-life house that the television show Monster House (2003) renovated to look like a mad scientist's lab. The various bottles and tubes in the background are alcohol dispensers in a special bar. Dr. Horrible's over-sized chair was an actual part of the homeowner's living room.
Time Magazine named this series the 4th best television series of 2008, despite the fact that it was created for, and only appeared on, the Internet. As of the issue's publication date (December 22, 2008), there weren't any plans to air the series on conventional television.
In the opening sequence, during which Dr. Horrible is talking directly to camera, many Joss Whedon fans mistakenly believed that the out of focus shape hanging in the window on the left was a model of the spaceship Serenity, a nod to Whedon's show, Firefly (2002). However, it was just a line of pots and pans hanging in the window.
In September 2009, a screening of "Dr. Horrible", followed by an interview of Joss Whedon by Ira Glass was held as a charity fundraiser for the nonprofit agency 826NYC, which provides free creative writing tutoring to children and teens. The choice of "Dr. Horrible" as a fundraiser for 826NYC is particularly apt; the storefront of the tutoring classrooms is a real business called The Brooklyn Superhero Supply Company, which sells such "superhero necessities" as capes, secret identity kits, "the world's first pair of continuous-use, non-invasive Invisibility Detection Goggles," and bottles and cans purporting to contain concepts including chaos, antimatter, and immortality. All store proceeds go to 826NYC.
The trivia item below may give away important plot points.
Australia seems to be the standard price for world domination. In Dr. Horrible's Sing-Along Blog, Dr. Horrible expects that his plans to rule the world may upset the love of his life, Penny. But he thinks that by giving her Australia, her tears will dry and she will therefore be more cooperative. In Superman II, Lex Luthor offers to cooperate with General Zod's plans to rule the world and expects to be given Australia in exchange for his efforts.