Count Theodosius (Latin: Comes Theodosius) was a senior military officer serving in the Western Roman Empire. He is also known as Flavius Theodosius or as Theodosius the Elder, distinguishing him from his son, the Roman emperor Theodosius I. He was granted the title of Count of the Britains (Comes Britanniarum) for his work there putting down the Great Conspiracy. He afterwards fought against the Alemanni and in Mauretania.
There is some evidence that Flavius Theodosius's father was called Flavius Julius Honorius, and his uncles Flavius Julius Gerontius and Flavius Julius Eucherius. He himself was called Flavius Julius Theodosius, claimed descending from the gens Julia through Gaius Julius Caesar's cousin Sextus Julius Caesar. Probably sometime in the late 330s or early 340s he married Flavia Thermantia. By her, he had at least two sons, Honorius and Theodosius (afterwards Emperor Theodosius I), born at Cauca (modern Coca, Segovia) in Spain. The family were Orthodox Christians.