Historical people

• Julius Caesar Drusus, son of the Emperor Tiberius, nicknamed "Castor"
• Castor of Rhodes, a Greek grammarian and rhetorician
• Saint Castor, name of several Christian saints, such as Castor of Apt
• A family name.

Fictional people

• Castor (mythology), one of the Gemini twins
• Castor Oyl, a fictional character in the Popeye cartoons and brother of Olive Oyl.
• the villain in the movie Face/Off, Castor Troy, portrayed by Nicolas Cage before the surgery and John Travolta after the surgery.
• One of the Spartan's allies in the game Spartan: Total Warrior.

Science and Technology

• Castor (star), α Geminorum
• Castor (software), a data binding framework for Java
• Castor bean, a poisonous spurge seed
• Castor oil, the oil of the castor bean
• Castor oil plant, the plant from which the castor bean grows
• Castor wax, a type of wax produced from castor oil
• Castor angle, alignment in the vertical longitudinal plane of a motor vehicle's wheels (misspelling of caster)
• CASTOR at CERN is the acronym for CERN Advanced STORage manager, a data storage system used at CERN, Geneva, Switzerland. CERN is the European Laboratory for the Research in Particle Physics.
• CASTOR, an acronym for "Centauro And Strange Object Research," a forward CMS calorimeter
• CASTOR is the acronym for Cask for storage and transport of radioactive material (containers used to transport highly nuclear waste)
• Castor, the genus name of (and in many Romance languages the word for) the beaver
• the Castor (rocket stage)
• a variant spelling of caster, a type of wheel
• on the Saturnian moon Janus (moon)
• a South Devon Railway 4-4-0ST steam locomotive of the South Devon Railway Eagle class

Music

• Castor (band), an independent rock band from Champaign, IL
• Castor Cracking Group, a demo group from Sweden active on ZX Spectrum

Places

• Castor, Alberta, Canada
• Castor, Cambridgeshire, England
• Castor, Louisiana, United States
• Castor (mountain), in the Pennine Alps
• Castor Bay in North Shore City, Auckland, New Zealand
• Castor Creek in Louisiana, United States
• Castor River (Missouri)
• Castor River (Ontario)
• an old name for Caistor St. Edmund, in Norfolk, England

HMS Castor

• HMS Castor was a 36-gun fifth-rate captured from the Dutch in 1781 by HMS Flora. One month later she was captured by the French Frippone off Cadiz.
• HMS Castor was a 32-gun fifth-rate launched in 1785. She was briefly in French hands in 1794, but was recaptured. She was sold in 1819.
• HMS Castor was a 26-gun fifth-rate launched in 1832. In 1860 she became a training ship. She was sold in 1902.
• HMS Castor was a C-class light cruiser launched in 1915. She was sold in 1936.