The correct answer to this open question is the following.
You did not mention who were the 3 kings discussed. So we are going to choose three kings to answer on the following terms.
The three major kings were King David(Judaism), Constantine(Christian), and Tariq Bin Zayad(Islam).
King David(1004-970) had a great influence on the people of Israel. His monotheistic belief impacted the Hebrew people. He was a great leader and a fierce warrior that won many battles that made him conquer many lands that were inherited by his son Solomon.
Roman Emperor Constantine( 306-337) instilled Christianity in the Empire after a dream where he was told by an Angel to convert to the Christian religion and many triumphs in battle may come. Man historians agree that Constantine, more than a believer in this faith, used Christianity as political propaganda to conquer, domain, and control the enormous territory.
Muslin Emperor Tariq Bin Zayad(670-720) has been considered one of the most important kings of the Muslim Empire. He was a great conqueror and he wanted to spread the monotheistic belief in prophet Mahoma in all his territories. He spread Islam through vast regions, including modern-day Spain.