Welf II (1072 – 24 September 1120, Kaufering), or Welfhard, called Welf the Fat, was duke of Bavaria from 1101 until his death. In the Welf genealogy, he is counted as Welf V.
Welf was the oldest son of Welf I, Duke of Bavaria, and his wife Judith of Flanders. In 1089, he was married to Matilda of Tuscany, who was 26 years older, in order to strengthen the relation between his family and the pope during the Investiture Controversy between king and pope. During King Henry IV's Italian campaign of 1090, Welf and Matilda fought against the King.
Since Matilda had secretly transferred her property to the Church before her marriage, Welf left her in 1095 and, together with his father, changed sides to King Henry IV, possibly in exchange for a promise of succeeding his father as duke of Bavaria.
After his father's death in 1101 Welf indeed inherited the office of duke of Bavaria. He continued his alliance with the kings; he did not remarry and died childless in 1120. Welf was buried at Weingarten Abbey.