The Alt-Oldenburger and Ostfriesen are representatives of a group of horse breeds primarily from continental Europe called heavy warmbloods. The breed has two names because the same horse was bred in two regions in the most north-western part of Germany: East Frisia and the former grand duchy of Oldenburg. The name "Alt-Oldenburger" – alt meaning "old" – simply distinguishes this horse from its descendant, the modern Oldenburg, which is bred for sport.

The AO/OF is bred by preservationists to fit the pre-World War model. Unlike the registries of the sport horses that followed them, their studbook is partly closed. However, external evaluation and performance testing of the breeding stock is still a key element in these registries.

The damp, low-lying region of Germany which lies between the Weser River and the Ems River is called Ostfriesland ("East Friesland"). It borders the Netherlands, and is part of a greater region traditionally known as Frisia. Frisia is characterized by the languages and dialects of the peoples who settled it, but also by its low-lying, coastal geography. In the west, it includes what are now the Dutch provinces of Friesland and Groningen; centrally, the Oldenburg region of Lower Saxony, and its northeastern region includes much of what is now Schleswig-Holstein to the border of Denmark. Frisia is the region best known for heavy warmbloods.

The word "Oldenburg" was first mentioned in reference to a town in 1108, and has had many meanings over the centuries. The name applies both to the city of Oldenburg, and also the surrounding rural district, and historically a state or Grand Duchy.

Prior to the 17th century, the horses of Oldenburg were of the same types found throughout Europe in the Middle Ages: small, hardy farm horses, smooth-stepping saddle horses, quicker "coursers", and a very few highly prized, powerful destriers. However, as the availability of firearms grew, heavily armored knights and their heavy mounts became impractical "relics of the past."

The Spanish horses, ancestors of the Andalusian, the Danish Fredriksborg, and the Neapolitan horse were particularly popular among the German nobility during the 17th and 18th centuries. As they collected these stallions, the residents bred them to their heavy mares, setting a foundation we would identify today as "baroque". From this base of thick, primarily dark-colored horses, the Groningen, Friesian, East Friesian, and Oldenburg would eventually be born.

The horses of Oldenburg have never had a State Stud, and they first gained recognition under Anton Günther (1583–1667), Count of Oldenburg, who is said to have taken great personal interest in the breeding of horses. Count Anton Günther returned from a trip lasting several years with a number of horses he admired in Spain, Italy, Turkey, and Poland. Later, a gift of Oldenburg horses kept the Count of Tilly from sacking Anton Günther's dominion.

While the breeding of horses in Ostfriese and Oldenburg was driven primarily by the nobles, without the aid of a studbook registry, the world's first ever stallion Körung occurred in the region. In 1715, Georg Albrecht Prince of Ostfriese adopted this practice of rigorous evaluation of potential herd sires. The Körung process spread to Oldenburg in 1755 even though state-mandated stallion inspections were almost 100 years in the future. The results were excellent, and the products were in high demand and exported for carriage driving.