In medieval Japan, a shugo, or "military governor," was a title granted to certain powerful warlords by the military dictator of Japan (the "Shogun"). The shugo was nominally in charge of protecting law and order for one of the imperial provinces of Japan. In some cases, the same warlord would be appointed shugo for several provinces, in which case a shugodai ("deputy shugo") would be appointed for each province, and in later years, some shugo were in charge of only part of a province.
The post of shugo was originally created in the late 1100s by the very first shogun, Minamoto Yoritomo, along with the similar post of jitō at the local level, in order to superimpose a military bureaucracy under his own direct control over the existing civil bureaucracy, and thus give the new shogun "boots on the ground" in every province in Japan. By the mid-Muromachi Period (1400s), however, many of the shugo increasingly became absentee title-holders, residing in lavish mansions in the capital at Kyoto and emulating the lifestyle of the Imperial Court, while real power increasingly fell to the shugodai back in the provinces. Some shugo remained active in military affairs however, and eventually became daimyo warlords during the chaotic Sengoku Period, creating independent states which they ruled over with absolute authority.
These daimyo are often called "shugo daimyo" to indicate their roots in the shugo system. Many of the earliest Sengoku daimyo were shugo daimyo, but over time, most of these early daimyo were overthrown by their subordinates, in a process known as gekokujō, literally "the low overthrowing the high.