"The one Who was and is and will be" in the Avesta is a recurring phrase that the scholars have shown its older usage in other Indo-European languages. In Pahlavi writings, this phrase sometimes describes God. There is a similar expression in Manichean writings. This article is a brief search on the history of these Zoroastrian and Manichean expressions.
Ghaem Maghami, S. A. R. (2021). "The one who was and is and will be". The Quarterly Journal Ayeneh-ye- Pazhoohesh, 32(189), 83-89. doi: 10.22081/jap.2021.71411
MLA
Seyed Ahmad Reza Ghaem Maghami. ""The one who was and is and will be"", The Quarterly Journal Ayeneh-ye- Pazhoohesh, 32, 189, 2021, 83-89. doi: 10.22081/jap.2021.71411
HARVARD
Ghaem Maghami, S. A. R. (2021). '"The one who was and is and will be"', The Quarterly Journal Ayeneh-ye- Pazhoohesh, 32(189), pp. 83-89. doi: 10.22081/jap.2021.71411
VANCOUVER
Ghaem Maghami, S. A. R. "The one who was and is and will be". The Quarterly Journal Ayeneh-ye- Pazhoohesh, 2021; 32(189): 83-89. doi: 10.22081/jap.2021.71411