The future Thai king Mangrai was born on October 2, 1238 in Ngoen Yang (present day Chiang Saen) Thailand on the Mekong River, a son of the local ruler Lao Meng and his wife Ua Ming Chommueang, a princess from the Tai Lue city of Chiang Rung, which is now called Jinghong, in Sipsongpanna (Xishuangbanna), China.

In 1259, Mangrai had succeeded his father to become the first independent king of the unified Tai city states in northern Lanna and what is now northern Laos.

Seeing the Tai states were disunited and in danger, Mangrai had quickly expanded his kingdom by conquering Muang Lai, Chiang Kham and Chiang Khong and initiating alliances with other states.

He founded the city of Chiang Rai in 1262 as his new capital in the Kok River basin.

He also seems to have been operating around this time in the area of Fang in the Upper Kok Valley.

Mangrai first made peace in 1280 between King Ngam Muang of Phayao and King Ram Khamhaeng of Sukhothai, who had seduced the former's queen.

The three Kings had then entered a pact to defend their lands against the expanding Mongol Empire.

While still living in the area of Fang, he had been visited by merchants from the Mon kingdom of Haripunchai (Haripunjaya, now known as Lamphun).

Hearing of the wealth of that kingdom, he determines to conquer it, against the advice of his counselors.

As it is thought impossible to take the city by force, Mangrai sends a merchant named Ai Fa as a mole to gain the confidence of its King Yi Ba.

In time, Ai Fa becomes the Chief Minister and manages to undermine the King's authority.

In 1281, with the people in a state of discontent, Mangrai defeats the Mon kingdom and adds Haripunchai to his kingdom.

Yi Ba, the last king of Hariphunchai, is forced to flee south to Lampang.