C
- John Cadbury — opened his shop in 1824 which became the company Cadbury
- Julius Caesar — the month of July, Caesar cipher, the titles Czar, Tsar, and Kaiser, the Bloody Caesar cocktail. An urban legend also erroneously credits Julius Caesar as having given his name to the Caesarian section; the two are likely unrelated, however.
- John Calvin, 16th century theologian — the religious doctrine of Calvinism; Calvin's name (with Thomas Hobbes) inspired name of the Calvin and Hobbes comic strip
- Caesar Cardini, restaurateur — Caesar salad
- Horatio Caro — Caro-Kann Defence
- Gian Giacomo Girolamo Casanova — casanova, a womanizer
- Sam Carr, neighbour of David Berkowitz also known as "Son of Sam" — Son of Sam law
- René Descartes, also known as Cartesius — Cartesian coordinate system
- Hendrik Casimir — Casimir effect
- Laurent Cassegrain - Cassegrain reflecting telescope
- Jean Dominique Cassini - Cassini division
- Empress Catherine I of Russia - Yekaterinburg
- Augustin-Louis Cauchy — List of things named after Augustin-Louis Cauchy
- Eduard Čech - Čech cohomology, Čech complex, Čech homology, Stone–Čech compactification
- Anders Celsius — degree Celsius (unit of temperature) Celsius (Moon crater)
- Ceredig — son of Cunedda — Cardigan
- Clyde Cessna — Cessna Aircraft
- Carlos Chagas — Chagas disease
- Subrahmanyan Chandrasekhar — Chandrasekhar limit, Chandra X-ray Observatory
- Jean-Martin Charcot, French neurologist — Charcot-Marie-Tooth disease; Maladie de Charcot, the French name for motor neurone disease
- King Charles I of England — North Carolina and South Carolina
- Charles IV, Holy Roman Emperor — places called Carlsbad, Karlstein Castle, Karlovy Vary, Charles University, Charles Bridge, asteroid 16951 Carolus Quartus
- Charles VI, Holy Roman Emperor — château Karlova Koruna
- Jacques Charles and Joseph Louis Gay-Lussac — Law of Charles and Gay-Lussac (frequently called simply Charles' Law)
- Bobby Charlton — the "Bobby Charlton" comb over hairstyle
- Augustin-Louis Cauchy — List of things named after Augustin-Louis Cauchy
- Nicolas Chauvin — chauvinism
- Vitaly Chekhover — Chekhover Sicilian
- Pavel Alekseyevich Cherenkov — Cherenkov effect
- Louis Chevrolet - founder, Chevrolet
- Jesus Christ, "The Saviour" — El Salvador, Christianity, Christmas
- Saint Christopher — Saint Kitts and Nevis
- Walter Chrysler — founder of Chrysler, DaimlerChrysler, Chrysler Building
- Alfred Chuang — the third letter of the company name BEA Systems, is taken from Alfred, a co-founder
- Alonzo Church — Church-Turing thesis, Church-Turing-Deutsch principle
- Cincinnatus, Roman statesman — Cincinnati, Ohio (indirectly)
- André Citroën - founder, Citroën
- Senator Claghorn, regular character on the Fred Allen radio show — Foghorn Leghorn, Warner Bros. cartoons
- Claudius, Roman emperor — the city of Kayseri, formerly Caesarea Mazaca, in Turkey
- Ruth Cleveland, daughter of Pres. Grover Cleveland — Baby Ruth candy bars
- Bill Coleman — the first letter of the company name BEA Systems, is taken from Bill, a co-founder
- Edgard Colle — Colle System
- Samuel Colt — Colt revolver
- Christopher Columbus — Egg of Columbus; many places and territories, see Columbus, Colombia, Colombo, British Columbia in Canada
- Arthur Compton — Compton effect
- Confucius — Confucianism
- Constantine I - Roman Emperor who in 330 moved the capital of the Empire to Constantinople
- Captain James Cook — Cook Islands; Cooktown (Queensland); James Cook University (Townsville); Cook (suburb of Canberra; co-named for Sir Joseph Cook); Cooks River; Cook (Federal electorate); James Cook University Hospital (Marton, Middlesbrough, England); Aoraki/Mount Cook; Cook Strait
- Gaspard-Gustave Coriolis — Coriolis effect
- Charles-Augustin de Coulomb — coulomb — unit of electric charge, Coulomb's law
- Michael Cowpland — founded the software company Corel (from Cowpland's Research Laboratory). Cowpland also co-founded the PBX Design / Build Company Mitel with Terry Matthews. (Mitel stands MIke and TErry's Lawnmowers)
- Thomas Crapper - Crapper
- Seymour Cray — Cray Research
- Hans Gerhard Creutzfeldt and Alfons Maria Jakob — Creutzfeldt–Jakob disease
- Burrill Bernard Crohn — Crohn's disease
- Cunedda — Gwynedd
- Marie and Pierre Curie — curie, unit of radioactivity, curium, chemical element
- Pierre Curie — Curie point
- Harvey Cushing — Cushing Disease, a pituitary tumor producing adrenocorticotropic hormone that causes excessive cortisol production
- Harvey Cushing — Cushing's Syndrome, a clinical condition characterized by excessive production of cortisol
- Saint Cuthbert ("church of Cuthbert") — Kirkcudbright
- Saint Cyril - Cyrillic alphabet
Read more about this topic: List Of Eponyms (A-K)