Founding teacher of Yokoji-Zen Mountain Center and the Zen Center of Los Angeles, Hakuyu Koun Taizan Maezumi Roshi was one of the most significant Zen practitioners of the twentieth century. During the last thirty-five years of his life, spent in the United States, he taught countless Westerners the subtle art of Zen meditation and practice. He was known to tell his students not to go searching for this thing called "Zen", but instead to develop an appreciation for their own lives. In his words, "all of us are equally absolute, equally precious, equally splendid, wherever we are at this moment."

Maezumi Roshi was ordained as a Soto Zen monk at the age of eleven. He received degrees in Oriental Literature and Philosophy from Komazawa University and studied at Sojiji, one of the two main Soto monasteries in Japan. He received Dharma transmission from Hakujun Kuroda Roshi, in 1955. He also received approval as a teacher (Inka) from both Koryu Osaka Roshi, and Hakuun Yasutani Roshi, thus becoming a Dharma successor in three lines of Zen.

He transmitted the Dharma to twelve successors: Bernard Tetsugen Glassman, Dennis Genpo Merzel, Charlotte Joko Beck (deceased), Jan Chozen Bays, John Daido Loori (deceased), Gerry Shishin Wick, John Tesshin Sanderson, Alfred Jitsudo Ancheta, Charles Tenshin Fletcher, Susan Myoyu Andersen, Nicolee Jikyo Miller, and William Nyogen Yeo. In America, Maezumi Roshi ordained 68 Zen priests and gave the lay Buddhist precepts to over 500 people. As a major contribution to the transmission of Buddhist teachings to the West, Maezumi Roshi was instrumental in bringing to realization the formation of the Soto Zen Buddhist Association (SZBA) of American Soto Zen teachers. Maezumi Roshi also promoted exchange programs among priests and lay practitioners between the United States and Japan.

At the age of 64 Maezumi Roshi died suddenly in Tokyo, Japan in the early morning hours of Monday, May 15 (Japanese time), 1995.

When Yokoji was founded, the formal name of the temple was Dounzan Yokoji. Zan means mountain and Doun refers to the honorary founder, Shiomi Doun Roshi. As Doun Roshi had vowed to open a certain amount of temples in his lifetime, Maezumi Roshi helped him fulfil his vow by naming him the founder of Yokoji.