Dr. Horrible's Sing-Along Blog is a 2008 musical comedy-drama miniseries in three acts, produced exclusively for Internet distribution.

Filmed and set in Los Angeles, the show tells the story of Dr. Horrible (played by Neil Patrick Harris), an aspiring supervillain; Captain Hammer (Nathan Fillion), his superheroic nemesis; and Penny (Felicia Day), a charity worker and their shared love interest.

[6] It also won a 2009 Creative Arts Emmy Award for Outstanding Special Class – Short-format Live-Action Entertainment Programs.

Dr. Horrible films an entry for his video blog, giving updates on his schemes and responding to various emails from his viewers.

Asked about the "her" that he often mentions, he launches into a song about Penny, the girl he likes from the laundromat who only knows him as his civilian alter ego Billy.

The letter informs Dr. Horrible that his application for entry into the League will be evaluated based on his next heinous crime ("Bad Horse Chorus").

The following day, Horrible prepares to steal a case of wonderflonium for his time-stopping Freeze Ray by commandeering the courier van with a remote control device.

Penny appears asking him to sign a petition to turn a condemned city building into a homeless shelter ("Caring Hands").

Captain Hammer appears and smashes the remote control receiver, inadvertently causing the van to veer towards Penny.

Under Penny's influence, Captain Hammer launches a crusade to help the homeless and clean up the city's structural issues.

Waiting at the laundromat for an absent Billy, Penny ponders her relationship with Hammer while Dr. Horrible goes into seclusion to build a death ray ("So They Say").

At the opening for Penny's new homeless shelter, Captain Hammer makes a speech that degenerates into condescending self-praise ("Everyone's a Hero").

Penny, embarrassed and disillusioned, quietly tries to leave, but Horrible appears and renders Hammer motionless with his freeze ray.

Dr. Horrible taunts the shocked crowd and reveals his completed death ray ("Slipping"), but hesitates before killing Hammer, fearing what Penny will think if she sees.

Hammer suddenly breaks free from his paralysis and punches Horrible across the room, damaging the death ray.

He picks up the death ray and prepares to use it on Horrible, but the damaged device explodes[9] and causes Hammer pain for the first time in his life.

Horrible fears he has vanquished his nemesis without committing the murder required by the League, but then discovers Penny fatally impaled by shrapnel from the exploding death ray.

Horrible realizes that Penny's death counts as the required murder, and that the infamous act has made him a true villain.

Dr. Horrible's Sing-Along Blog Soundtrack made the top 40 Album list on release, despite being a digital exclusive only available on iTunes.

Buffy and Angel writers Doug Petrie and Drew Goddard cameo as supervillains Professor Normal and Fake Thomas Jefferson, respectively.

As a web show, there were fewer constraints imposed on the project, and Whedon had the "freedom to just let the dictates of the story say how long it's gonna be.

If the Internet and iTunes releases were successful enough, Whedon planned to greenlight an official DVD, which would include some "amazing extras".

[20] The musical's fansite launched in March 2008 (despite the official site containing nothing more than a poster at the time) and was the first place to publicly release the teaser trailer three months later on June 25, 2008.

[25] On June 2, 2009, a new release of Dr. Horrible's Sing-Along Blog was produced by New Video Group, which included the same materials as the Amazon DVD but was distributed through regular retail outlets.

The first three were through its online comics anthology Dark Horse Presents, the fourth was a special release as part of the "One Shot Wonders" series.

[39] In November 2018, a new comic was released written by Joss Whedon titled Dr. Horrible: Best Friends Forever with art by Jose Maria Beroy and Sara Soler.

[48] In November 2010, Cult Classic Theatre in Glasgow, Scotland, performed the first official UK production of Dr. Horrible's Sing-Along Blog.

[52] In a review for the Los Angeles Times, Robert Lloyd writes: "It is a sweet, rather sad piece that — like the songs, by Whedon and his brother Jed, which are at once mock-heroic and actually heroic, mock-moving and moving in fact — works both as parody and as a drama.

In 2009, Joss Whedon announced at San Diego Comic-Con that a sequel was in the works and that it might be presented as either another web series or as a feature film.

[61] While promoting Marvel Studios' The Avengers in March 2012, Whedon said he and the writers involved in Dr. Horrible would be working on writing the script during the 2012 summer.