The Shōgun was the name given to the military dictator of Japans from 1185 to 1868. Shōguns were the de facto rulers of the country, mostly self-appointment, but sometimes the Emperor would hold a ceremony for them.
Sho means commander and Gun means troops. The Shogun was therefore the commander of the troops. Shoguns were disciplined, fierce, always in control, and always very militaristic. They are depicted in shunga art as strong but also violent, and many wars were fought under the rule of the Japanese Shōguns.
Shōguns were painted in shunga art, going back to at least six centuries. To have Shōguns in your home, on a painting or an image, depict strength and courage. They are often shown in battle, carrying swords, with many troops around them. They are also oddly depicted in erotic situations, with geishas or concubines.