Astrid is a young girl Viking who is determined to be the best in her dragon training class. However, her attempts are thwarted by Hiccup, who uses unorthodox methods in passing the class. She begins suspecting that Hiccup is cheating somehow, and follow him to a cove on day--only to find out that he has been keeping his own dragon, Toothless. While at first she is terrified of the dragon, she slowly warms up to Toothless after Hiccup invites her on a flight.

After Toothless is captured, Astrid helps HIccup rescue him and eventually helps the rest of the Vikings defeat the "queen" of the dragons. By the end of the film, she has developed a romantic relationship with Hiccup, and has a dragon of her own.