This is the fifth in the Ultraman series with sixth Ultra brother from M78 nebula arriving on Earth to battle the monsters.
Taro is traditionally a name given to the first son in Japan, and Ulraman Taro's name reflects this as he's the first son of Ultra Father, and Ultra mother.
Kotaro Higashi (Saburo Shinoda) is a young man aspiring to become a champion boxer. One day he gets injured during an attack by a monster. Two ladies treat his wounds. One turns out to be his future house mate, and the other is none other than the Ultra mother herself disguised as an earthly mother. She gives him the badge that allows him to transform into Ultraman Taro. He later joins ZAT, a special squad formed specially to battle monsters.
This is the first Ultraman series where Ultra mother appeared, and the existence of Ultra "family" became clear.
The quality of the series is not the best of Ultraman series, but it's not the worst either. The realistic approach of Ultra Seven gradually gave way to atmosphere that catered to small children starting with Ultraman Jack. In this series, there're no seriousness to the story, and the stories are geared to entertain children. But it does try to show how a good person should behave, and ZAT, Ultraman Taro, and even the children in the story tries to be a role model for the viewing children.
Out of the Ultraman that was made in the '70s, this one is the most campy. If you're an adult viewer, this Ultraman is not recommended for viewing.