Veralidaine Sarrasri: played by Alexis Bledel, Daine is a teenage girl with magical power which allows her to speak to and turn into animals. She is traveling to Carthak as a part of a political delegation from her adopted country, Tortall.
Numair Salmalin: played by Rodrigo Santoro, Numair is one of the world's most powerful mages and Daine's teacher. He has a nasty past with the Emperor of Carthak--he had to flee to Tortall for his life.
Alanna the Lioness: played by Bryce Dallas Howard, Alanna is part of the Tortallan delegation to Carthak as an ambassador.
Emperor Ozorne: played by Taimak Guari, Ozorne is Carthak's emperor and not a little crazy. He seems to think that his people should worship HIM, not the gods. Among other things.
Rikash: played by Ben Foster, Rikash is an irascible Stormwing--not quite Daine's friend, not quite her enemy.
Lindhall Reed: played by Timothy Olyphant, Lindhall is one of Numair's oldest friends and a mage in Carthak. A northerner in origin, he hates slavery and secretly smuggles slaves out of Carthak.
Kaddar: played by Mehcad Brooks, Kaddar is Ozorne's nephew and the current heir to Carthak's throne. He squires Daine around the city and palace, and smuggles slaves out of the country with Lindhall in his spare time.
And that's how Diana casts it. All images pulled from Google and Wikipedia.