Constantius I (Flavius Valerius Constantius; 31 March 25 July 306) was a Roman emperor. He ruled as "Caesar" from 293 to 305 and as "Augustus" from 305 to 306. He was the junior colleague of the "Augustus" Maximian under the Tetrarchy and succeeded him as senior co-emperor of the western part of the empire. Constantius ruled the West while Galerius was "Augustus" in the East. He was the father of Constantine the Great and founder of the Constantinian dynasty. After his death he became known as Chlorus (, 'the Green'), but the nickname does not appear in records before the sixth century.