Ahura Mazda is the creator God in Zoroastrianism. His name is most commonly translated as Lord of Wisdom, or Lord Wisdom.
Zoroastrianism is named after the Prophet of the faith, Zoroaster, also known as Zarathustra. According to legend, he came in contact with a shining being, many say an angel and that angel led him into the presence of Ahura Mazda. Ahura Mazda reportedly taught him the principles of what would come to be Zoroastrianism. Zoroaster described Ahura Mazda as an uncreated spirit. In other words, a spirit without beginning, without a creator. This distinction is important as it places Ahura Mazda into the category of The One. He exists beyond time and is the source of all existence. Without him, nothing exists. He is eternal and changeless.
In Urianism, Zoroaster is said to be an incarnation of the Archangel Hanael. He is credited by Spirit (in Urian communications) to be the founder of the first monotheism.
Zoroastrianism is/was practiced by people who were born into the faith. You have to be/had to be born a Zoroastrian to BE Zoroastrian. Today there is a lot of controversy around the idea of conversion. Many traditional Zoroastrians believe that both your mother and father have to be ethnically Zoroastrian in order to be Zoroastrian. However, according to the Parsi priestly hierarchy in Bombay, conversion is possible.
If you want to know more about that you can read the following article by Hannah Michael Gale Shapero
ANCIENT IRANIAN RELIGIONS: ZOROASTRAIN
Conversion to Zoroastrianism
Another article on the subject from the Encylopedia Iranica, can be found here: