Emperor Wen of Sui

Regent for his infant grandson, he took the Northern Zhou throne in 581 and conquered the Chen in 589, ending the longest division in Chinese history. The institutions he built — the Three Departments and Six Ministries, an examination route into office, the equal-field system, granaries, a rebuilt Grand Canal — were taken over wholesale by the Tang and lasted a thousand years.

He was also frugal to the point of meanness and deeply suspicious, and he chose the wrong son at the end of his life.

Empress Wenxian — Dugu Qieluo — made him swear at fourteen that he would father no child by another woman, and he never did. She sat in on government, and the court called them the Two Sages, a century before the phrase was used of Wu Zetian.