A toshiyori (年寄), also known as an oyakata (親方), is a sumo elder exercising both coaching functions with active wrestlers and responsibilities within the Japan Sumo Association (JSA). All toshiyori are former wrestlers who reached a sufficiently high rank to be eligible to this status. The benefits are considerable, as toshiyori are guaranteed employment until the mandatory retirement age of 65 and are allowed to run and coach in heya (sumo stables), with a comfortable yearly salary averaging around ¥15,000,000 (US$137,000).

Originating from a tradition dating back to the Edo period, the position of toshiyori is founded on a system set up at a time when several sumo associations managed Japan's professional wrestling. To become a toshiyori, a former wrestler has to meet both established and public criteria and be part of a system recognized as opaque. Involving the spending of several million yen to inherit the rights to become a trainer, this system has undergone numerous reforms, firstly limiting the number of people eligible to hold management positions in the Japan Sumo Association, and then more or less partially reforming the system as a whole. Despite this, the position of toshiyori is still highly sought after by wrestlers, maintaining a high level of speculation over the right to practice.

Distributed within the Sumo Association to occupy specific functions, toshiyori also respond to a clear hierarchy, at the top of which are the elected directors of the Japan Sumo Association.

There are many terms used to define a trainer in the world of professional sumo. Alongside the official term of toshiyori (年寄), a sumo coach is also referred by the terms of oyakata (親方) and shishō (師匠).

Prior to its appearance in the sumo world during the 17th century, the term toshiyori was used primarily in the Edo period and before to refer to central and provincial government administrators as well as community leaders, with a meaning of "senior citizen". For its part, the term oyakata is a suffix used in the honorific system as an honorific attached to proper nouns. Initially the term referred to a person with the status of surrogate parent or big brother, and used to refer to an apprentice master.

The term shishō, or stablemaster, refers specifically to a toshiyori who owns and runs a heya, or sumo stable. At the top of the heya social pyramid, he takes on a paternal role for all under him. Of all the coaches potentially present in the stable, he alone is the owner and therefore the highest authority in communal life.

The function of sumo elder was born with the organization of the first tournaments authorized by the municipal administrations of major Japanese cities. Although sumo as a sport goes back several centuries, its professionalization dates back to the beginning of the Edo period. During this period, the peace established by the Tokugawa shogunate led to the vagrancy for many samurai who had lost their social standing with their previous masters, who had been deposed or killed so that the shogunate could assert itself. Masterless samurai, called rōnin, had no choice but to put their martial art skills to good use in street sumo tournaments, called tsuji-sumo (辻相撲; lit. 'street-corner wrestling'), for the entertainment of passers-by. Eventually, the mix of disgraced rōnins with the commoners who took part in the contests of strength of the street tournaments created many conflicts over betting money. Tense brawls, even deaths, sometimes occurred. During the Keian era, public order became so disturbed that, in 1648, the Edo authorities issued an edict banning street sumo and matches organized to raise funds during festivities. In 1684 (Jōkyō era), a sumo rōnin named Ikazuchi Gondaiyū obtained permission to lift the sumo ban edicted by the Edo authorities. Because he allowed the return of matches by proposing a new etiquette associated with the conduct of fights, Ikazuchi was recognized as a key interlocutor by the authorities, which earned him a tournament organizer's license referring to him as a "toshiyori", one of the first mentions of the term in sumo. Later, the term was definitively adopted by his successors in the organization of tournaments where it came to be used specifically to refer to the masters at the head of groups of wrestlers who took part in charity tournaments in support of sanctuaries, and who were responsible for enforcing discipline during festivities and avoiding fights. To organize the tournaments, the toshiyori went under their former ring names on delegations to submit petitions to the shogunate officers and secure authorization to hold the tournaments. In parallel with the emergence of toshiyori in the Edo-based sumo association, the associations in the cities of Osaka and Kyoto were organized around elders known as tōdori (頭取).

During the Genroku period, the various sumo groups were no longer scattered across the country, but rather concentrated in the major cities of Edo, Osaka and Kyoto. These groups were self-organised under the leadership of elders, who welcomed the wrestlers into their homes, which took the name of heya (meaning "fraternity house") in reference to the rooms in which these elders met to organise matches during tournaments. In 1719, the Edo municipal authorities issued an edict prohibiting all sumo groups that had not become professionalized from taking part in charity tournaments. The direct consequence of this edict was the disappearance of the elders who came directly from the ranks of the rōnins, and only the elders who were wrestlers who had retired from the ring remained. The organization based on Edo municipality edicts was gradually implemented in the other major sumo associations based in Osaka, Kyoto and Nagoya during the eighteenth century. With the reform of the charity tournaments, the number of elders grew significantly, tripling in Edo between 1720 and 1780. During the Hōreki era, masters began to inherit and assume the names of their predecessors, each share being attached to the ring name of the wrestler who had established himself as a trainer and passed on his license to one of his apprentices. The practice of becoming an elder until death or final retirement also became widespread around this time. From the 1750s onwards, the practice of welcoming novice wrestlers into the elders' homes became more widespread, these houses becoming the first examples of stables.