How do you unlock Professor Flitwick in Lego Harry Potter years 1 4?

To unlock Professor Flitwick in Lego Harry Potter Years 1-4, you need to first complete the fourth year at Hogwarts. Once you have done this, you can go to the Great Hall and talk to Professor Flitwick. He will give you the task of collecting ten books for him. The books are located all over Hogwarts and can be found by exploring the different rooms and areas. Once you have collected all the books, return them to Professor Flitwick and he will unlock the character for you.