Shokan was the general name of an officer governing Japanese shoen (manor) entrusted by the lord of the manor. Some Kaihatsu ryoshu (reclaimers) donated manors and the lords of the manor kept them on as shokan to manage the manor, also the lords of the manor sent their retainers to the local manors to reinforce their influence.
Between the late tenth century and the eleventh century in the mid Heian Period, Tato (powerful peasants) cultivated menden (reclaimed land exempt from charges) which was allowed by Kokushi (provincial governor), and privatized it. (These farmers were called 'Kaihotsu ryoshu' [reclaimers]). However, the legal basis of their property rights was fragile and it was possible for kokuga (provincial government offices) to seize the properties. Thus, tatos donated their land to the powerful nobles or powerful temples in the central government in order to be exempt from charges and to keep the power of their land. A lord of the manor who received a donated manor was called Ryoke, and as Ryoke appointed Kaihatsu ryoshu as Geshi/Gesu (lower ranked officer), Kumon (a local shoen official below the gesu in rank) or Suito (local shoen official below the gesu and kumon in rank), Kaihatsu ryoshu could keep their positions as manager of the manor. Shokan is a general name including Gesu and Kumon. Generally, shokan received land from a part of the manor. The land that shokan received was exempt from charges and shokan could keep all of the harvest. Geshi/Gesu (lower ranked officer) were named, distinct from the lord of the manor, as Joshi (Geshi's superior), and the name of Kumon was derived from their role, which was management of books and records.
Ryoke often donated their manors to the imperial or sekkan families and the lord of the manor at the top of the relationship was called Honke (head family). The person who controlled the manor among the Honke and Ryoke was Honjo (proprietor or guarantor of the manor). To take greater control of manors, Honjo often sent down their retainers to supervise Gesu and Kumon. The retainers who were sent down to local manors were called Azukaridokoro/Azukasso (deputy of the 'Shoen' manor lord). Azukaridokoro was also one of the shokan. Later, some Kaihatsu ryoshu (including Gesu and Kumon) were appointed as Azukaridokoro.
As there was no clear legal rule, control and management of manors were not stable and depended on the authority of the lord of the manor. Therefore, conflicts over the control, management and boundaries of the manors often occurred between other shokans and kokuga (provincial government offices), and the shokans handled these problems. At that time, many lower ranking aristocrats with samurai rank who could not get posts in the central government went down to the provinces, and shokan established heirachichal relationships with them in order to solve conflicts over the manors. Some shokans became samurai.
(Not all shokan became samurai.)
In the Kamakura era, some shokan were admitted as Gokenin (an immediate vassal of the shogunate in the Kamakura era） or Jito (manager and lord of the manor) by Kamakura bakufu (Japanese feudal government headed by a shogun). This meant that the protection by the lord of the manor was not enough and shokan began to rely on the Kamakura bakufu which rose as a new authority. Shokan began to disrespect the lord of the manor (Honjo) and rob Honjo of their interests. From the beginning of the Muromachi era, shokan transformed into kokujin (local samurai) as local lords. Even so, shokan had existed with the manorial system until the Sengoku period, however, they disappeared because manors were dissolved by Taiko-kenchi (the land survey of Hideyoshi TOYOTOMI). But some words such as "Shoya" (village headman) and "Myoshu/Nanusi" (village headman) remained in the Edo era as the remnants of shokan.