Theodor is a masculine given name. It is a German form of Theodore. It is also a variant of Teodor.

• Theodor W. Adorno (1903–1969), German philosopher, musicologist, and social theorist
• Theodor Aman, Romanian painter
• Theodor Blueger, Latvian professional ice hockey forward for the Pittsburgh Penguins of the National Hockey League (NHL)
• Theodor Burghele, Romanian surgeon, President of the Romanian Academy
• Theodor Busse, German general during World War I and World War II
• Theodor Cazaban, Romanian writer
• Theodor Eicke, German SS general
• Theodor Fischer (fencer), German Olympic épée and foil fencer
• Theodor Fontane (1819–1898), German writer
• Theodor Seuss Geisel, American writer and cartoonist, known by the pseudonym Dr. Seuss
• Theodor W. Hänsch (born 1941), German physicist
• Theodor Herzl (1860–1904), Austrian-Hungary Jewish journalist and the founder of modern political Zionism
• Theodor Heuss (1884–1963), German politician and publicist
• Theodor Innitzer (1875–1955), Austrian Catholic cardinal
• Theodor Kittelsen (1857–1914), Norwegian painter and illustrator
• Theodor "Teddy" Kollek (1911–2007), mayor of Jerusalem from 1965 to 1993
• Emil Theodor Kocher, Swiss medical researcher, recipient of the Nobel Prize in Physiology or Medicine
• Theodor Mommsen (1817–1903), German writer and historian, Nobel Prize in Literature 1902 laureate
• Theodor Holm Nelson, American pioneer of information technology, philosopher of computer science, and sociologist, known as Ted Nelson
• Theodor Paleologu, Romanian politician
• Theodor Pallady, Romanian painter
• Theodor Reuss, German occultist, freemason, illuminati, martinist, rosicrucian, theosophist, journalist, singer and founder of Ordo Templi Orientis
• Theodor Rosetti, Romanian politician
• Theodor Șerbănescu, Romanian poet
• Theodor S. Slen (1885–1986), American judge, lawyer, and politician
• Theodor Stolojan, Romanian politician
• Theodor George Henry Strehlow, Australian anthropologist and linguist, known as Ted Strehlow
• Theodor Svedberg, Swedish chemist, Nobel Prize in Chemistry laureate
• Theodor Zwinger, Swiss scholar
• Theodor Jan Haraldsson, known by his stage name Theoz, Swedish influencer and singer

• Theodore (name)
• Teodor