The earliest reference to kundalini yoga https://www.julianalucky.com/story dates from around the beginning of the first millennium B.C. According to the Upanishad records found, at that time it was a philosophy and science that studied the energies of the human body. In the first classes, the masters talked about their spiritual knowledge and their students listened. There was no physical exercise. Jesus and 
Buddha acted in a similar way later on. The body movements came later.
For thousands of years kundalini yoga was a practice for the chosen few. Only those who were trained for years and then initiated could gain access to the knowledge. Some secret society of Indian elite was formed, inside which traditions of kundalini were kept and passed on for thousands of years. It was thought that the general public was not ready for such knowledge.
Kundalini yoga managed to go beyond the circle of initiates only in 1968. Yogi Bhajan left Punjab for Toronto, where he began to teach this discipline to all comers, founding an institute for the study of kundalini and training teachers in various countries of the world. It was Bhajan who defined kundalini yoga as the science of uniting the finite with the infinite. He was the one who started the history of the triumphal procession of this discipline throughout the world.