The Manx name Costain derives from Thorstein and is of Viking (Norse) origin. Theoretically every Costain in the world is related because the name comes from just one clan that established itself on the IoM around 1100 years ago. So Costain (the global building firm) for example started in a small workshop on the Colby Main Road in the Isle of Man. Costain/Thorstein is thought to mean either Son of Thor, or Thor's stone - depending on translation. If Son of Thor then clearly the clan was important in Viking society. If Thor's stone, the implication is similar: that the clan would probably have been responsible for preparing Thor's stone for blood and other sacrifices to the Norse god of thunder - again a highly respected/revered position in Viking society. Costains still own and farm much of the south of the Isle of Man - alongside the Gawne, Clucas and Watterson families.

People named Costain

• Molly Costain Haycraft
  Molly Costain Haycraft
  Molly Costain Haycraft is a Canadian author. She was born in Toronto, Canada, and spent her childhood in Philadelphia, where her father, the well-known novelist Thomas B. Costain, was an editor for The Saturday Evening Post. She is the author of several novels about women in English royal history...
  
  , Canadian, author.
• Albert Costain
  Albert Costain
  Sir Albert Costain was a Conservative Party politician in the United Kingdom. He was Member of Parliament for Folkestone and Hythe from 1959 to 1983, preceding future Conservative leader Michael Howard....
  
   (1910—1987), British, politician.
• Thomas B. Costain
  Thomas B. Costain
  Thomas Bertram Costain was a Canadian journalist who became a best-selling author of historical novels at the age of 57.-Life:...
  
  , (1885-1965), Canadian, journalist, author.