Pegasi

Pegasus ponies, or Pegasi, are ponies characterized by their wings and their ability to fly, walk on clouds, and control the weather.

Development and nomenclature
Pegasus ponies were introduced shortly after Earth ponies in the original My Little Pony toy line. On the show, they are called either Pegasus ponies or Pegasi, and mostly "Pegasus" for a single pony, though "Pegasus pony" is also used, as specified in the article ponies. Lauren Faust, the show's developer, stated that the Pegasus ponies have a passive kind of magic that allows them to walk on clouds and manipulate the weather.

Pegasus ponies are derived from Greek Mythology, notably the tales surrounding the eponymous flying horse, Pegasus, who was a white horse with wings. Pegasus is also the name of one of the 88 modern constellations.

Origins
The Pegasus tribe was one of the three founding groups of Equestria, as depicted in Hearth's Warming Eve, and were responsible with maintaining the weather in return for food that was harvested by the Earth Ponies. The Pegasus tribe was led by Commander Hurricane, who is played by Rainbow Dash in a historical reenactment. In the reenactment, Commander Hurricane wears battle armor and calls the Pegasi "a mighty tribe of warriors".

Before the three pony tribes united under a single nation, Commander Hurricane originally intended to name their new home "Pegasopolis".

Physical and magical traits
Pegasus ponies demonstrate great speed and agility in the air in multiple episodes. However, in the episode Fall Weather Friends, Rainbow Dash is equally matched on the ground with Applejack, an earth pony, during an "Iron Pony competition". In the episode Sonic Rainboom, Pegasus ponies naturally walk, sit, and lay on clouds, but unicorns and earth ponies cannot do so. Twilight Sparkle casts a temporary spell that allows her non-Pegasi friends and herself to walk on clouds. Gilda, a griffon, also stands on clouds in Griffon the Brush Off. In May the Best Pet Win, it shows several other creatures capable of flight perch on clouds.

The sonic rainboom is an aerial display that is first featured in the episode Sonic Rainboom. Pinkie Pie describes it thus: "The sonic rainboom is legendary! When a Pegasus like Rainbow Dash gets going so fast... boom! A sonic boom and a rainbow can happen all at once!" Rainbow Dash performs the sonic rainboom three times in seasons one and two: once as a filly in a flashback in The Cutie Mark Chronicles, once in Sonic Rainboom, and once at the conclusion of A Canterlot Wedding - Part 2.

Social responsibilities
In Sonic Rainboom, the main characters visit the Cloudsdale weather factory. They walk through a chamber where Pegasi handcraft snowflakes, an open area where Pegasi mix up rainbows and finally the cloud-making department.

At the beginning of the episode Hurricane Fluttershy, Rainbow Dash hosts a mandatory meeting for all Ponyville Pegasi, in which she states, "A team of Pegasi combine their wing power to create a jumbo tornado, powerful enough to pull water out of the local reservoir, and funnel it all the way up to Cloudsdale." This, she explains, supplies Cloudsdale and all of Equestria with rainwater. Rainbow Dash also stresses that the ponies' combined power must exceed a minimum of "eight hundred wing power". During training, Twilight Sparkle uses an "anemometer" to gauge wingpower. Rainbow Dash's score on the anemometer was 16.5 wingpower and Fluttershy's post-training score was 2.3 wingpower.

In the episode Winter Wrap Up, Rainbow Dash leads the weather team during the annual Winter Wrap Up. The team, which wears blue vests, consists mainly of Pegasus ponies. In the song that shares its name with the event and episode, the weather team clears the skies of clouds to let the sun warm up the land and melts the snow. Rarity mentions that the team also "guides the birds back north for the spring". On a frozen lake, Twilight Sparkle encounters Pinkie Pie, an Earth pony, who is helping the weather team by acting as a "lake scorer". Pinkie Pie cuts squares in the ice with her ice-skates and explains to Twilight that it helps the rest of the Weather team break the ice layer.

Residence
Pegasus ponies live in Ponyville, where all three types of ponies live, and Cloudsdale, which is exclusively populated by Pegasus ponies since only they can walk on clouds. Fillydelphia is mentioned in Hurricane Fluttershy to have a Pegasus pony population as well. No Pegasus ponies have yet been seen in Manehattan, which is only shown in The Cutie Mark Chronicles. In the episode It's About Time, Rainbow Dash mentions a town called "Los Pegasus". Canterlot is almost devoid of Pegasus ponies, with the exception of the royal guards who pull Princess Celestia's chariot in Swarm of the Century. Another pair of Pegasus royal guards carries Twilight Sparkle to Ponyville in a similar chariot in the Friendship is Magic, part 1. Also, a trio of them attack Nightmare Moon in Friendship is Magic, part 2.