Stephanorhinus kirchbergensis, also known as Merck's rhinoceros (or, less commonly, the forest rhinoceros), is an extinct species of rhinoceros belonging to the genus Stephanorhinus that lived in Eurasia from the end of the Early Pleistocene (around 800,000 years ago) until its extinction in the Late Pleistocene (surviving until at least 40,000 years ago and possibly later). Its range spanned from Western Europe to East Asia. Among the last members of the genus, it co-existed alongside Stephanorhinus hemitoechus (the narrow-nosed or steppe rhinoceros) in the western part of its range.

Merck's rhinoceros was a large rhinoceros, with a body mass in the range of 1,500–3,000 kilograms (3,300–6,600 lb), with a 2016 study estimating an average body weight of around 1,800–1,900 kilograms (4,000–4,200 lb). A particularly large specimen from Poland reached an estimated height at the withers of 1.82 metres (6.0 ft). It is one of the largest species of Stephanorhinus, exceeding S. hundsheimensis and S. hemitoechus in size. The bones of the skeleton are robust and massive. The skull of Merck's rhinoceros is elongated, with the septum nasalis ossified only towards its anterior (front) end. The mandibular symphysis is relatively long and the mandible has a horizontal high, thick branch.

Like other Stephanorhinus species, Merck's rhinoceros lacked incisor teeth on the upper and lower jaws, similar to living black and white rhinoceroses, with its teeth consisting of three premolars and three molars in each half of the upper and lower jaws.

The enamel of the teeth is very thick, and often bright coloured and smooth, with very thin or absent coronal cement. The buccal (cheek-facing) sides of the teeth often have sub-vertical bluish lines. Tooth dimensions are highly variable in comparison to other Stephanorhinus species. The upper teeth, especially the molars, are much higher towards the buccal side than to the lingual (towards the tongue) side. The ectolophs of the first and second upper molars have shallower folds, especially the fold between the paracone and mesostyle, than those of S. hemitoechus, resulting in a less pronounced undulation. In comparison to other species of Stephanorhinus, the premolars of S. kirchbergensis are mesially (towards the front of the tooth) broad and relatively lingually short. The upper premolar ectoloph folds are shallow, and have narrow anterior valleys. The ectoloph curves strongly mesially and often distally (towards the hind portion of the tooth) towards the inside of the tooth. In both upper molars and premolars, the metalophs and the protolophs are distinctly bulbous. The lower premolars and molars are similar and hard to distinguish.

The species was named by Georg Friedrich von Jäger in 1839 for Kirchberg an der Jagst in Baden-Württemberg, Germany where the type specimens of the species had been found. It is often known in English (and equivalents in other languages) as Merck's rhinoceros after Carl Heinrich Merck, who gave the initial name to the species in 1784 as Rhinoceros incisivus, that is now considered a nomen oblitum, and who after a widely used junior synonym of the species, Rhinoceros merckii (historically several alternate spellings) was named by Johann Jakob Kaup in 1841.

Merck's rhinoceros belongs to the genus Stephanorhinus, which first appeared in Europe during the Late Pliocene, around 3.5 million years ago, and is known from fossils across Eurasia. Mitochondrial and nuclear genomes obtained from Merck's rhinoceros suggest that its closest living relative is the Sumatran rhinoceros (Dicerorhinus sumatrensis), though it shares a closer common ancestry with the extinct woolly rhinoceros (Coelodonta antiquitatis), from which it suggested to have diverged around 5.5 million years ago.

Relationships among Late Pleistocene and modern rhinoceros genera, based on nuclear DNA, after Liu et al., 2021:

Bayesian morphological phylogeny, after (Pandolfi, 2023) Note: This excludes living African rhinoceros species.