Who was the first ruler of Abbasid Dynasty?

al-Saffāḥ

The first Abbasid caliph, al-Saffāḥ (749–754), ordered the elimination of the entire Umayyad clan; the only Umayyad of note who escaped was ʿAbd al-Raḥman, who made his way to Spain and established an Umayyad dynasty that lasted until 1031.

Who founded Abbasid dynasty?

Abbasid dynasty