As a child, I thought castor oil was an extract from animals (beavers, specifically). I suppose I can blame that on childhood logic after learning the French name for beaver. It was only much later when I learned that it was a plant derivative from the species in today's photograph, Ricinus communis, or the castor bean plant. Wikipedia provides a detailed summary of the chemistry and uses of castor oil. In particular, the use as an instrument of intimidation is both interesting and disgusting.
Despite the many uses of castor oil, Ricinus communis also happens to contain a deadly poison, ricin. The entire plant is poisonous if ingested, but the seeds are particularly potent; one chewed seed may be enough to kill a child, see: ricin toxin. The Cornell web site also contains a page about the plant itself, Ricinus communis, where it explains that ricin is water-soluble and hence will not find its way into castor oil during the production process provided proper precautionary measures are taken (thanks to Anne for the link, as well).
The widespread tropical and subtropical cultivation of Ricinus communis has made it difficult to determine its original distribution. The Handbook of Energy Crops, in addition to providing extensive details about cultivation and production, suggests Ricinus communis is African in origin. The comprehensive photographs of the species available on MissouriPlants.com are accompanied by a write-up suggesting an Asian origin.