What is one fundamental belief of Zoroastrianism?

Zoroastrianism centers on the belief in one supreme deity, Ahura Mazda, who represents the ultimate truth and goodness. This monotheistic perspective is foundational to the religion, distinguishing it from polytheistic traditions that worship multiple gods. Ahura Mazda is seen as the creator of the universe and the source of all good, embodying the essence of truth and light. Followers of Zoroastrianism commit themselves to the principles of good thoughts, good words, and good deeds, which align with the teachings of Ahura Mazda.

The other beliefs mentioned, such as reincarnation or karma and dharma, are descriptive of other spiritual traditions and not intrinsic to Zoroastrian doctrine. Zoroastrianism does not incorporate the concept of multiple gods but instead emphasizes the singular nature of Ahura Mazda as the ultimate and only deity worshipped by its adherents.