" We Are Number One " is a song from the Icelandic children's television series LazyTown , composed by Máni Svavarsson. The song was featured in the twelfth episode of the show's fourth season, entitled "Robbie's Dream Team", which is the 103rd episode overall. 
The song gained popularity in September 2016, when a remix was uploaded onto the YouTube channel SiIvaGunner ,  where various parodies have been subsequently uploaded since,  as well as proper cover versions by bands such as comedy punk group The Radioactive Chicken Heads. 
The official music video has over 36 million views on YouTube as of 10 October 2017. It is the most viewed video of the LazyTown YouTube channel.
Robbie Rotten, the primary antagonist of LazyTown , attempts to teach his "dream team" of villainous accomplices (three fictional doppelgänger actors called Bobbie, Tobbie, and Fobbie Rotten) how to successfully catch a superhero (specifically Sportacus).
Robbie Rotten demonstrates multiple methods to his team: an overhead cage attached to a tree (which ends up trapping Robbie), a large butterfly net, a false apple containing enough sugar to induce an overdose and consequently, temporary unconsciousness, to the sugar-averse Sportacus, a somewhat small fishing net, and banana peels intended to cause Sportacus to slip, but instead causing Robbie's own team to do so.
The sugar apple proves to be an effective trick, successfully sedating Sportacus and giving Robbie and his team a chance to put him in a portable cage. Robbie's three teammates relocate the trapped Sportacus to Robbie's underground headquarters while Robbie stays on the surface to set up a cannon, revealed in the full episode to be the way Robbie intends to run Sportacus out of town. However, his plans are thwarted when Stephanie and Stingy open the base's periscope and uses the cylindrical inside of it as a means of transporting a real apple to Sportacus. The apple rolls undetected by the now-sleeping Bobbie, Tobbie and Fobbie, with Sportacus reaching it and regaining his power, of which he was deprived by the sugar overdose. He then uses his reclaimed strength to break free from the cage and coax his three captors to play sports with him on the surface of LazyTown.
Robbie watches as his previous companions play sports with Sportacus, and, out of apparent anger, walks over to them disregarding a bucket on the ground. This bucket is kicked, hitting and triggering Robbie's cannon and thus blasting Robbie away from the scene via the cannonball. The video ends with Bobbie, Tobbie, and Fobbie accidentally falling into a trapping pit constructed by themselves to capture Sportacus, thus enforcing for a final time the clumsiness of the team.
The song originally had the working title called "Villain Number One" before it was changed to "We Are Number One". During production there were many lyrics that did not get approved, many of these lyrics have Robbie singing something different than what he actually sung in the final version. These lyrics first surfaced to the public when it was revealed by Máni during the live stream that Stefán held on Facebook on 11 December 2016, at the Icelandic studios where the show was filmed.  These unused lyrics were released to the public on SoundCloud by user 8847444 on 13 December 2016. 
Two years after the LazyTown episode aired, "We Are Number One" became an Internet phenomenon due to Robbie Rotten's performer Stefán Stefánsson having announced that he had been diagnosed with pancreatic cancer.   A campaign was created by Mark Valenti, head writer for LazyTown , on the crowdfunding platform GoFundMe  to pay for Stefán's living costs while he was too unwell to work and the creators of these parodies used their videos to raise awareness for the campaign.   As of 20 December 2016, the campaign had surpassed its $100,000 goal. 
To thank the contributors, Stefán held a live stream on Facebook on 11 December 2016, where he performed "We Are Number One" with the other actors (Björn Thors, Bergur Þór Ingólfsson, Snorri Engilbertsson) from the original music video  which was later uploaded to his personal YouTube channel. 
TeamFourStar's "DragonBall Z Abridged" series created an instrumental parody version of the song titled "TFS Tunes: We Are Number One (But It's Perfect)," if sung along with the closed captioned lyrics would say "we are Perfect Cell" rather than "we are number one." A short clip of the song was used in the background of their 58th episode in the series.
Typically, these parodies take the form of the original music video edited in some irregular and often highly complex way, most of them with the title "We Are Number One but..." which is a meme, followed by the changes from the original, which would occasionally be placed in the video description due to their length, like "every time they say one the video gets more high pitched".  This type of remix was common in 2016, particularly during the year's waning months; a The Verge article described "We Are Number One" and other, similar remixes as "weird solipsistic creation[s]". 
The official LazyTown YouTube channel has posted several videos relating to the song, including an hour loop of the original song, an instrumental version, a reversed instrumental version, every "one" being replaced by "The Mine Song" (another song from the series, also with numerous parodies, which later became an internet meme in November 2016), a compilation of the songs with other well-known songs from the series (however, in PAL speed) and the full episode that the song appeared in, "Robbie's Dream Team" from 2014.  The original tracks (otherwise known as the "stems") used in composing the song were released shortly after. 
A petition was set up to have Stefán perform the song to represent Iceland in the Eurovision Song Contest, receiving over 12,000 signatures.  The petition wanted him to participate in the 2017 edition, but Stefán didn't apply, acknowledging that he was unlikely to do so, as recovering from his cancer was a bigger priority.
- Stefán Karl Stefánsson - lead vocals
- Bjðrn Thors - backing vocals
- Snorri Engilbertsson - backing vocals
- Bergur Þór Ingólfsson - backing vocals
- Máni Svavarsson - synthesisers, piano, drum machine