Al-Saffah

Abu al-ʿAbbās ʿAbd Allāh ibn Muḥammad ibn ʿAlī ibn ʿAbd Allāh ibn al-ʿAbbās (Arabic: أبو العباس عبد الله ابن محمد ابن علي‎; 721/722 – 8 June 754), known by his laqab al-Saffāḥ (Arabic: السفّاح), was the first Caliph of the Abbasid Caliphate, one of the longest and most important caliphates in Islamic history.

His laqab al-Saffāḥ means "the Blood-Shedder". It may refer to his ruthless tactics, or perhaps it was used to intimidate his enemies. It was during his inaugural homage as Caliph, delivered in the Great Mosque of Kufa, that he called himself "al-Saffah" ("the Blood-Shedder"), and this title stuck to him due to his massacre of the Umayyads.

Source: Wikipedia — https://en.wikipedia.org/wiki/Al-Saffah