Gru is a ROUND character because we see more than one side of his personality. He is mean and selfish at times, but we see his softer side when he falls in love with his new daughters. Throughout the movie, we are able to see his character being sinister and wicked as well as protective and willing to do the right thing.
Gru is also a DYNAMIC character because he does undergo a huge personality change throughout the movie. He is evil at the beginning, but Gru's morals, values, and personality completely change by the end of the movie.