The dragon who serves as Twilight Sparkle’s assistant is Spike.
Spike is a purple baby dragon who accompanies Twilight from the beginning of “Friendship Is Magic.” He serves as her “number one assistant,” helping organize her schedule, take notes, and support her studies. Although Twilight is his employer and mentor, she also treats him as her adoptive younger brother.
Spike’s most distinctive practical ability is sending written messages through his fire breath. In the early seasons, he burns Twilight’s letters to Princess Celestia, magically delivering them and receiving replies. This makes him an important link between Twilight, her friends, and the royal court.
Viewers sometimes confuse Spike with Garble or Smolder, who are also dragons in the series, or with Discord, who is a draconequus rather than a dragon. Spike also has a major personal storyline: he struggles with being a dragon raised among ponies, develops a crush on Rarity, and eventually becomes a friendship ambassador and Twilight’s royal adviser.