Fluttershy is one of the six main characters in My Little Pony: Friendship Is Magic series. As her name implies, she is incredibly shy and soft-spoken. She lives in a cottage on the edge of the forest, where she cares for various animals, most notably Angel, a little bunny who despite his cunning and mischievious demeanor, seems to care very deeply for Fluttershy.
Fluttershy also has a strong side, as shown in Dragonshy (when she reduces a full-grown dragon to tears) and also in Stare Master (when she stares down a cockatrice as it's turning her to stone, causing the creature to run away in fear).
She is also a pegasus, but she prefers to stay on the ground, as she's not a very strong flier. Plus, her wings will clamp down and cause her to fall when she's frightened (as seen in Dragonshy).
While normally very sweet to all creatures, she doesn't seem to handle rejection well. In 'The Best Night Ever' episode, all she wants is to meet the creatures in Princess Celestia's garden. When they all run and hide from her, she goes to great lengths to get them to come out, including setting traps. When this fails to work, she bursts into the castle, all of the animals running away from her and causing destruction and chaos. Fluttershy has completely lost it by this point, proclaiming, "You're going to LOVE ME!!!"