He became the undisputed Persian ruler in 554 B. C ... He treated the conquered people fairly by allowing them to worship the religion of their choice.

Cyrus the Great became the undisputed Persian ruler in 554 B. C.

Explanation:

Cyrus the Great is one of the greatest rulers of Persia and is responsible for the formation of the borders of the historical Iranian region and also was responsible for the foundation of the first Persian empire.

He was an incredibly forward thinking ruler who made a codified law in his domains and unified the country under his rule and conquered new territory where he followed a liberal rule.

The people in his dominion were free to practice their religion and propagate it and only had to follow the codified rules that were universal.