Buddha rediscovered the path of Dhamma leading to the eradication of universal suffering. Practicing Vipassana, he penetrated the veils of ignorance, delusion, and illusion. He discovered the Law of Dependent Origination (paticcasamuppad), the chain of cause and effect conditioning the universe. Whatever arises, arises due to a cause; when the cause is eradicated there can be no resulting effect. Therefore, by totally eliminating the cause of suffering, one can attain real happiness, real liberation from all misery.
With this realization, he penetrated the illusion of solidity in mind and matter, dissolved the tendency of his mind to cling and crave, and realized the unconditioned truth. The subtlest defilement of his mind were washed away. All the shackles were broken. No craving remained for the future; his mind became free from all attachments. Siddhattha Gotama attained Supreme Enlightenment, experiencing the ultimate truth in all its purity, and became a Sammasambuddha.
With great compassion he spent forty-five years showing the path of Dhamma and thus helped millions of people to come out of their misery.