Tao Yuan can be called Dao Yuan or En Tao and he is the father of Tao Ren and Tao Jun. He is the source of hatred of Ren.
Tao Yuan's Different Names
Original English Dub
What Uncle En implies in the dub: this suggests that Tao Yuan in the dub anime of Shaman King is the uncle of Jun and Ren Tao. It is unknown why the dub change Tao Yuan's family relationships.
Tao Yuan is the father of Ren Tao and Jun Tao in the manga and Japanese anime version.
Tao Yuan has force his family mostly Ren Tao and Jun Tao to avenge the Tao family because of the persecution of the family due to the hatred of shamans in China. Tao Yuan's family has done many evil deeds but Tao Yuan's father states that their deeds are not that evil. Tao Yuan's father tells Manta that good and evil has lost meaning in an ever changing world. The Tao family has kill many people so they can use their corpses as Jiang-Si (manga) or Kyonshi (anime). The Tao family are like necromancers who control corpses.
His role in Shaman King
Tao Yuan is responsible for Ren Tao's suffering and personality. He forces Ren to destroy and cause more suffering. After his son, Ren, has lost the match to Yoh Asakura in the last pre-liminary match, Ren Tao is a changed man who decides to change his goal (only dub: rule the world) to ending the cycle of hatred and vengeance. When Ren fights his father with the assistance of Yoh Asakura, Bokuto no Ryu, Jun Tao, Lee Pailong, and Horohoro, Tao Yuan's oversoul loses mana due to Tao Yuan's will has waivered. Ren defeats his father because his Tao is pure and his will is stronger. When Ren leaves his family in China for the Shaman King fight in America, Tao Yuan rides his dragon and throws his treasured sword to Ren.