The Most well known aspect of Bagua Zhang is walking the circle while executing the forms. Bagua is unique in this respect. It has its roots in Daoism, where walking the circle and meditating were combined. The circle being a radius distance from your opponent and the forms are attack and defence. The circle walking forms are practiced on a circle diameter between 6' and 9' or 2 to 3 meters.
Bagua Zhang was created or passed onto Dong, Hai Chuan. What is known about him is that he was highly skilled. Among his early students were those of the palace guards. Those he taught outside of the palace, were taught based on their abilities. Hai Chuan would only take on as students those who had already mastered a style, adapting his teaching to their knowledge and ability. One thing that remains a constant is the 8 mother palms, taught by almost all of the current lineages of Bagua. The differences of each lineage beyond the 8 Mother Palms is a result of the adaptive teaching of Dong, Hai Chuan. The connection to the Yi Ching is a result of the 2nd or 3rd generation students who studied it and applied what they learned to their respective lineage of Bagua Zhang as a continuance of their studies.
One of Dong, Hai Chuan's students was Cheng, Ting Hua who was the teacher of Sun, Lu Tang, one of the most famous practitioners known today.