A brilliant wizard who grew up on the stories of Starswirl The Bearded Caster was born as Caster Starlight in Canterlot. He spent his life following in the hoofsteps of his idol, studying every magic he could, from the mundane to the fantastic.
But his pursuit of knowledge has lead him into more bad situation than he could count. Despite being well versed in all manner of magic Caster is not without his faults. He tends to be vain with younger wizards, and shows off to impress them as he wants to be a hero like Starswirl was to him.
And tends to get lost in thought when a idea hits him, often ignoring others until forcfully brought back to reality.
At heart though he lives up to his name, and has lived and learned enough to see the best in the most dire problems.
His desire to do good is matched only by his skill.