Leung Yee-Tai was a boatman who steered his boat with a long pole. He was a master at using the long pole as a weapon.
He taught Wong Wah-bo the pole techinques in exchange for learning Wing Chun. And this is how the six and a half point pole form came into the Wing Chun system. The pole form was never originally in the system. According to legend, Wong Wah-Bo found that the pole fit the theories of Wing Chun and could be utilised as one of its weapons - along side the butterfly knives.
Wong Wah-Bo taught Leung Jan, who ended up becoming a legend in the Wing Chun system.