Soto Zen is a branch of Zen Buddhism that originated in Japan and is known for its emphasis on zazen, or seated meditation. It was founded by Dogen, a 13th century Buddhist monk and philosopher, who is considered one of the most influential figures in Japanese Buddhism.

Dogen was born into a noble family in Kyoto, Japan in 1200. At a young age, he became interested in Buddhism and began studying under the guidance of various teachers. However, he was not satisfied with the teachings and practices he encountered and embarked on a journey to China to study with the masters of the Chinese Chan school, which later became known as Zen in Japan.

During his time in China, Dogen studied under the guidance of Master Rujing, who introduced him to the practice of zazen. It was through this practice that Dogen experienced a profound awakening and returned to Japan to spread the teachings of Zen.

Soto Zen, as taught by Dogen, emphasizes the practice of zazen as the main path to enlightenment. Unlike other schools of Zen that focus on koan study or other forms of meditation, Soto Zen places a strong emphasis on shikantaza, or "just sitting" meditation. This practice involves sitting in a relaxed but alert posture, without any particular goal or object of concentration. Through this practice, one can cultivate a deep awareness and understanding of the present moment.

Dogen also emphasized the importance of everyday activities as a form of practice. He taught that zazen is not limited to sitting on a cushion, but can be applied to all aspects of daily life. This approach, known as "everyday Zen," encourages practitioners to bring mindfulness and awareness to all their actions, whether it be eating, walking, or working.

In addition to zazen, Dogen also emphasized the concept of "non-duality," which is the idea that there is no separation between the self and the world. This understanding is essential to the Soto Zen tradition and is embodied in Dogen's famous statement, "To study the Buddha Way is to study the self, to study the self is to forget the self, and to forget the self is to be enlightened by the ten thousand things."

In summary, Soto Zen is a branch of Zen Buddhism that emphasizes the practice of zazen and everyday mindfulness as the path to enlightenment. It is closely related to Dogen, who founded the tradition and emphasized the importance of zazen and non-duality in his teachings. Today, Soto Zen continues to be a popular form of Zen practice in Japan and around the world, with Dogen's teachings serving as a guiding force for practitioners seeking to deepen their understanding of the nature of reality and the self.