Spike is a baby dragon and secondary character in My Little Pony: Friendship Is Magic. He is Twilight Sparkle's assistant and one of her best friends. Spike was actually her entrance exam for Princess Celestia's magic academy, as she had to hatch him from his egg to pass. So needless to say, they've been together for quite some time. Twilight also seems to be the closest thing Spike has to a mother figure, something that becomes obvious when his jealousy of Owlysius gets the best of him and thinks Twilight doesn't love him anymore. Some of the actions he has displayed during the course of the show thus far exhibit his young age, he has proven himself to be a capable and reliable friend and assistant.
He also has a very puppy love-esque crush on Rarity, causing him to do whatever favor she sends his way. (Such as taking out her garbage, helping her gather gemstones, ect.) Rumor has it that we will see a Rarity/Spike episode this season. If I had to venture a guess, I'd say it will be a Valentine's episode.
But anyway, if you're a fan of the cutest baby dragon ever, please join the fanlisting and show your love!