Soka Gakkai's philosophical roots reach back to Shakyamuni, the founder of Buddhism. In his youth, Shakyamuni, or Prince Siddhartha as he was called at the time, became profoundly troubled by human suffering. He gave up his princely status at a young age and pursued the life of a religious mendicant in search of a solution to the various sufferings of life he witnessed, such as birth, old age, sickness and death. His eventual realization of the essential nature of reality is known as enlightenment and his subsequent teachings to help people overcome suffering are known as Buddhism.
To be able to transmit to people the enlightenment he had attained, Shakyamuni taught for 50 years, leaving behind many teachings. His earlier teachings, based in part on what his disciples could readily comprehend, aim to awaken people to the impermanence of all phenomena to free them from sufferings arising from self-centered attachments.
In the Lotus Sutra, preached toward the end of his life, however, Shakyamuni taught that the Buddha nature--potential for enlightenment--exists in all life. The development of this nature enables all people not only to overcome any and all sufferings but to live a fulfilled life actively interacting with others and the whole of society. The Lotus Sutra is a truly egalitarian* teaching that can have a profound and positive influence on people's daily lives.
*egalitarian - of or advocating equal rights for all.