Teen dragon that was adopted into a family of Canterlot ponies when he was a baby! He is level headed and very smart for his age, and is absolutely fascinated by the fancy hairstyles and unique magic of Canterlotian unicorns. He can not fathom why his big sister Twilight Sparkle doesn't ever bother to make her mane, and makes sure to fix it up for her every morning while she's eating her breakfast.
When him and his sister relocated to Ponyville, he very quickly became best friends with Rarity, not only because they're both at least part dragon but also because of their shared passion for fashion.
Spike is a teen dragon, so he grows Fast. He's expected to grow twice the size he is now, but it's not 100% as he may be a mixbreed of a guardian and sea dragon so he might even triple in size with age.