Human sacrifice was carried out by various nomadic herding peoples on the Eurasian steppe. The physical and literary evidence agrees: human sacrifices were made at funerals of some high-ranking people, kings or their equivalent. Most often, when there was human sacrifice, it looks like servants and warriors were sacrificed, presumably to accompany the dead king in the afterlife. According to written accounts, at least some of the time those sacrificed were volunteers - for example, at the funeral of the Cuman prince Jonah in 1241, eight warriors volunteered to be sacrificed.

Most of the known examples are Scythian. The first archaeological finds came as somewhat of a surprise to many, since it was widely assumed that Herodotus's description of Scythian human sacrifice was sensationalist propaganda. There are later examples too (e.g., Prince Jonah mentioned above), including sacrifices for some Mongol khans (Ogogei is reported to have sacrificed "40 noble, jewel-bedecked virgins" to the spirit of his father, Genghis Khan, and Hulegu's funeral involved human sacrifice). Sometimes, human sacrifice was on a large scale - over 300 people were sacrificed for the funeral of the Khitan khagan Abaoji, founder of the Liao Dynasty (but not his wife, although that would have been traditional - she reported sacrificed her right hand).

However, human sacrifice was uncommon, and appears to have been restricted to royal burials. Animal sacrifice was much more common, and many warrior burials included sacrificed horses (and no sacrificed humans). After horses, the next most common sacrificial animal might have been the dog. Royal burials typically included horse sacrifice. Horse sacrifice was widespread, beyond the steppe, and was also performed by sedentary peoples near the steppe (e.g., Lithuania (where horse sacrifice continued in state rituals for some time after the official adoption of Christianity) and Korea).

The above specific examples are from Christoph Baumer, History of Central Asia, volume 3, I. B. Tauris, 2016. Further examples are given in volume 1 (and perhaps volume 2, but I didn't check).

For discussion of examples from Scythian archaeology, see Renate Rolle, "Royal Tombs and Hill Fortresses: New Perspectives on Scythian Life:, chapter 17 in The Golden Deer of Eurasia: Perspectives on the Steppe Nomads of the Ancient World, The Metropolitan Museum of Art, 2006: https://www.metmuseum.org/art/metpublications/The_Golden_Deer_of_Eurasia_Perspectives_on_the_Steppe_Nomads_of_the_Ancient_World

A postscript: there are some steppe burials with 2 bodies: a man and a woman. These are sometimes assumed to be primarily male burials accompanied by a sacrificed widow. This might have been the case sometimes, but in at least some couple burials like this, the two inhumations were separated by many years, and the woman was much older at death. So some of these couple burials appear to be non-sacrificial family burials over time - widow sacrifice should not be the default assumption.