Ken Kitazawa is a one of the main characters in The Powerpuff Girls Z. He appeared since the beginning of the episode.  Ken is a young scientist and only son of Professor Utonium, he called him Professor than Dad. He one of the original character of Japan, Toei animation. 

Ken acts more mature than the Powerpuff Girls, sometime he does get more bossy and bosses them around. He sort of spoiled because of his father. Ken doesn't go to school because he already smart enough.