Gru is a villain. And when we meet him in Despicable Me he is on a quest to be the ultimate villain with a plot to steal the moon. He has an army of minions to help with his evil plots, as any good villain would. Along the way he meets and adopts Margo, Edith and Agnes who are originally supposed to help with his evil plan but eventually manage to transform Gru into a better person and a loving dad.
In Despicable Me 2, Gru has left his villain days in the past and is working on being a good dad and a legitimate business man. However after his minions are kidnapped and transformed into mutated purple monsters he is forced to rescue them from another villain. In our licensed Despicable Me costumes becoming Gru or one of his memorable minions is easy, even if being a super-villain is not.