The name Rainer comes from the Germanic name Reginar, composed of the two elements ragin ("advice") and heri ("army"). The name was brought to Britain by the Normans. Cognates:
- German: Rainer
- Scandinavian: Ragnar
- Danish: Regner
- French: Rainier
- Italian: Raniero
- Spanish: Rainiero.
People whose family name is or was Rainer include:
- Adam Rainer (1899—1950), Austrian dwarf and giant
- Arnulf Rainer (born 1929), Austrian painter
- Dachine Rainer (1921—2000), British poet and anarchist
- Friedrich Rainer (1903—1947), Austrian National Socialist politician
- Gerhard Rainer, Austrian bobsledder
- Luise Rainer (born 1910), German film actress
- Marie-Louise Rainer, Italian luger
- Reinhold Rainer (born 1973), Italian luger
- Roland Rainer (1910—2004), Austrian architect
- Thom S. Rainer (born 1955), U.S. Christian writer and speaker
- Wali Rainer (born 1977), U.S. football player
- Yvonne Rainer (born 1934), U.S. choreographer and filmmaker
