Iron Horn was the brother of Rain-in-the-Face, Hunkpapa, and the son of Chief Bear Face.

Photo by A. Gardner 1872, when Iron Horn was part of the Sioux delegation to Washington. — Dietmar Schulte-Möhring

This should be the Iron Horn who was a brother of Rain in the Face. There were six full-brothers, sons of the Hunkpapa Bear Face I (Mato Ite). The latter was a signatory as a warrior to the 1825 Hunkpapa treaty with the Atkinson-O'Fallon Commission. He must have been born about 1800. His sons were:

Red Thunder - born about 1827, this is LaDonna's ancestor
Bear Face II - born about 1830
Iron Horn - born about 1830
Rain in the Face - born about 1836
Little Bear - born ?
Shave Head - born ?

The family was a leading tiwahe within the Che-okhba or Droopy Penis band. The band occupied the place in the Hunkpapa camp-circle next to the Sore-Backs band, which suggests they may have been sister bands, one budded off the other. This is borne out by the fact that Running Antelope (born ca. 1820) and Cross Bear (born ca. 1846), who were heads of the leading Sore-Backs families, are both identified as 'brothers' of Bear Face II, Iron Horn, etc. In the case of Running Antelope, I suspect that his father and Bear Face I were brothers - hence the Lakota relationship as 'brothers'.

Iron Horn came to Ft Sully October 1865 to attend treaty talks as a Hunkpapa soldier. According to his own statement he was made a chief this same year - 1865. (Robert P. Higheagle to Stanley Vestal stated that IH was "not a chief at all", but conceded that he was the herald, eyanpaha, or camp crier of the Hunkpapas.) He signed the 1868 treaty at Ft Rice and was among the first Hunkpapas to settle at Grand River Agency - hence his role in the 1872 delegation and the Gardner portrait above. His brothers Bear Face and Red Thunder were also agency leaders by 1876, but IH stated in 1879 that his other 'brothers', naming Rain in the Face, Little Bear, and Cross Bear, were in Canada with Sitting Bull's people.

Check back to Tokayuspe's posting in the Hunkpapa bands thread, because he intimates that Long Dog and Iron Dog, Hunkpapa headmen in Canada with Sitting Bull, were also 'brothers' to "Rain", i.e Rain in the Face. I'm not sure how this relationship worked, but one hunch I'm working on is that these men's mothers may have been 'sisters' and belonged to the Wakan band of Hunkpapa. I would think that Iron Dog's and Long Dog's fathers belonged to the Talonapin, Raw Meat Necklace band. — Kingsley Bray