Herman is Carl's black-hearted, sadistic, evil ant brother and is the emperor of Antsylvania. He wants to use his massive armies to take over the world, which is something that he came quite close to doing. Despite his past failures, Herman refuses to let go of his ambitions, and his armies are always ready to march on a moment's notice.
Herman is considered a HUGE momma's boy, due to being Edna's favorite son for his successes. As shown in "Get Off My Back", his mother will either adore one or the other (when Carl put on his slippers of heart's desire, he reveals that he is always wanted his mother's love; when Edna was giving Carl tons of attention, she treated Herman the way she treats Carl, with no love and belittlement) in just about every scene that Herman and Edna have been in together.
It has been hinted in "Dictator of the Year" that Herman is the eldest of the two. When Herman was born, Carl was nowhere to be seen (though the clip was showing Herman right after he was born, so Carl may not have been in the room at the time). Despite his small stature, Herman is one of the strongest individuals in the world and makes use of that fact in order to force people into doing what he wants.
He is very strong for his size (like other ants). He also can lift boulders and trees with no effort. He once used his strength to make a clap so strong it created powerful shockwaves. However, he has an allergy to Panda hair, that Master Yo has been used to stop him in his previous attempts.