Yasutsune "Anko" Itosu studied under Bushi Matsumura, as well as Nagahama of Naha and Gusukuma of Tomari. He was born in Shuri and served as secretary to the king. It is believed that he received the nickname Anko because he walked in a horse stance. He was approximately 5 feet tall and was known for his arm, leg and hand strength as well as his intuition. He had the ability to sense the attack and destroy it before it fully developed. He used to punch the stone walls that lined the roads. He is famous for developing the technique of "gripping" the ground. When a judoka challenged him to a match, he told the judoka he would concede the match if the judoka could move him. After 10 minutes of trying the judoka conceded. You can read the details on page 48 of O'Sensei's book. He believed that a karateka (karate student) should train intensely to develop one's physical strength, ability and spirit. A karateka should always be helpful and never fight.
Itosu was a legend in his own right, and is considered by many to be the "Father of Modern Karate-do". In 1901 he was instrumental in getting karate introduced into Okinawa schools, teaching at Shuri Jinjo Primary School, Dai Ichi Middle School and the Okinawa Prefectural Mens Normal School. He created the Pinan forms and introduced them as learning steps for children feeling that the other katas where too hard for children to learn. He is also credited with taking the large Naihanchi kata and breaking it into the Naihanchi Shodan, Nidan and Sandan katas we practice today. Itosu believed it was time for karate to go beyond the shores of Okinawa and wrote his famous letter of Ten Precepts in 1908. Read more about Itosu including his father's unique method of training him when he was young, his first encounter with Matsumura, his defense against 3 attackers, how Matsumura helped him with his cowardliness, and more starting on page 43 of O'Sensei's book.