Section of Zhang Lu's painting of Lü Dongbin, early 16th century.
Lü Dongbin was born in China about 796 CE. He was an important Daoist scholar, teacher, and author of religious texts; and he is the most famous of the Eight Daoist Immortals.
Certain legends surround the actual man. He is said to have been a heavy drinker and a womanizer, who by using his mastery of yin/yang and the five elemental energies (wu xing) was able to seduce many beautiful women. Eventually Lü Dongbin did obtain a higher level of being and became enlightened. For over a thousand years he has been worshipped as a Daoist deity.
He is depicted in art as being dressed as a scholar and often mounted on a tiger, the symbol of divine energy and power. He carried with him a white horse-hair whisk that bestowed upon him the power to fly through the skies and walk the clouds. (Other sources say to brush away ignorance.)
Lü Dongbin is also famous for his magical charms (yellow paper with sacred writings) that could ward off ghosts and demons. In the legends Lü used a double-edged sword called "The Demon Slayer" to capture, tame, or dispel all evil spirits. It also gave him the ability to hide in the heavens and render him invisible to evil spirits.
In Daoist traditions Lü Dongbin is thought to be mysterious, magical, and divine. His positive emotions embody courage, bravery, impartiality, and righteousness while he suppresses the negative feelings of sorrow despondency and misery. [All above text taken from http://www.northernshaolinacademy.com]
For Further Information:
Hirsh Diamant. About Qi, Lü Dongbin, Immortality, and Self-Cultivation.
New World Encyclopedia.
Northern Shaolin Academy, Audubon, PA. Meditation – Eight Immortals.
 ^ The name in pinyin is Lü Dòngbīn; in Traditional Chinese 呂洞賓; in Simplified Chinese 吕洞宾; in Wade-Giles Lu Tung-Pin. He was born Lu Yan (Lu is the family name and means a vibrating string sounding a musical note). Yan, the given name, may mean "cliff" or "rock." As an adult he was given the courtesy name Dongbin, (meaning "the guest of the cavern") In Daoist literature he is sometimes called "Ancestor Lü."