What do the early Shiite ghulat have in common with the notorious Umayyad governor of Iraq, al-Hajjaj b. Yusuf al-Thaqafi (r. 694-714)? Nothing much, except for their connection with the beliefs in the Greatest Name of God (ism Allah al-aʿzam). Al-Hajjaj and the ghulat stood on the opposite side of the political spectrum; several of the ghulat rebelled against the Umayyads, while al-Ḥajjaj formed their backbone. Yet, we have texts that ascribe to both sides the ability to wield power through the Greatest Name of God. In this paper, I will explore this unexpected connection and the beliefs in the Greatest Name of God in context of eighth-century Iraq. Through the case study of the Name, the paper will shed light on the interconnected cross-sectarian and cross-religious milieu of early Islamic and Late Antique Iraq. It is rather well known that the Greatest Name of God played a central role in the cosmology of some of the early Shiite ghulat, such as Bayan b. Sam’an or Mughira b. Sa’id. So Bayan claimed for instance that he could, through the Name, vanquish armies, and Mughira that he could revive the dead. But these accounts may raise doubts: to what extent can we rely on the later heresiographies for their reliable depictions? It is perhaps less known that al-Hajjaj b. Yusuf was another figure seen as able to wield the power of the Greatest Name of God. In one of the speeches ascribed to him, we see him addressing the rumors that he knows the Greatest Name of God: “You claimed that I know the Greatest Name, so why do you fight the one who knows while you are ignorant” (Ibn Abi al-Hadid, Sharh Nahj al-Balagha). But again, how reliable are Hajjaj’s speeches that have been written down only much later after he died? We need to set these texts in their broader context. In this paper, I will draw on different types of sources—heresiographical accounts about the ghulat, the speeches of al-Hajjaj, Sunni and Shiite hadiths, and Sufi literature—to explore the eighth-century beliefs in the Greatest Name of God. Furthermore, I will highlight Jewish and other Late Antique parallels. I will argue that the beliefs in the Greatest Name of God were not limited to the ‘extreme’ claims of the ghulat, but were part of the multicultural milieu of eighth-century Basra and Kufa.