Omar Khayyam is associated with the 11th-century calculation of the Jalali calendar used by Nowruz.
The Seljuk sultan Malik-Shah I commissioned a calendar reform in the 11th century, and Omar Khayyam was among the scholars involved. The resulting Jalali calendar used astronomical observations to regulate the solar year and improve the placement of Nowruz.
Khayyam is widely known today as a mathematician, astronomer, and poet. His calendar work is separate from the later development of the modern Solar Hijri calendar, which was adopted in Iran in the 20th century, but both systems share the solar New Year tradition.
Rumi and Ferdowsi were major Persian poets, while Avicenna was a physician and philosopher. None is the standard answer to the calendar-reform question.