In my paper I study the circumstances of composition, circulation, and transmission of a corpus of writings produced in eighth-ninth century Iraq by a group of Shi’is called “extremists,” or Ghulat, for their “extreme” devotion to the Imams. This Corpus comprises a number of cosmological-mythological writings that describe the Ghulat ideas about God, man, and the universe. The paper is based on all of their surviving writings, which comprise three categories of texts: previously published works that have been known for decades (such as Kitāb al-haft wa l-aẓilla, Kitāb al-ṣirāṭ, and Umm al-kitāb); works that have been published since 2006 as part of the series Silsilat al-turāth al-ʿalawī ― in their entirety or as fragments in later Nuṣayrī texts (e.g., Kitāb al-ḥujub wa l-anwār, Kitāb al-Kursī, and Bāṭin al-taklīf); and unpublished works surviving in manuscript (Kitāb al-ashbāḥ wa l-aẓilla). I begin by arguing for the existence of a unified “Ghulat Corpus” ― by showing that the presently known Ghulat writings were produced, circulated, and read in the same religious and social milieu, and contained a limited and continuously recycled inventory of cosmological themes. Through a close textual analysis, I trace the roots of the teachings of the Corpus in the eighth century Iraqi sectarian milieu, then look at the later trajectory of the transmission of Ghulat texts from Iraq to Syria by the Nusayris. I conclude the paper by a discussion of the position of the authors of the Ghulat Corpus in the Iraqi society of their time. Based on internal clues provided by their writings, and on the scant external evidence found in heresiographies and historical works, I attempt to understand their ethnic background and economic occupations, their relations with the Shi’i leadership, and the nature of their groups.