Derek is a fun, easy-going teenager. He's laid back and casual about almost everything--except, of course, most vampires. He doesn't take too many things seriously. He is very family-oriented, and was raised to respect family, friends, and community. He is extremely loyal. Especially to his friends. He is obsessed with cars. He is very cheerful and optimistic.
And, of course, he is absolutely gorgeous. =) For this reason, he can be sort of cocky. But he just so happens to be very sincere as well, which balances out any ego-bloating on his part.
Most of his friends call him wolf boy for his uncanny strength and abilities, but they don't know the half of it.