Simplify the following text for a Grade 6 native English-speaking person.
Original: Galerius ( Gaius Galerius Valerius Maximianus , ~ 260 â `` 5 May 311 ) , was Roman Emperor from 305 to 311 .
Simplified: Gaius Galerius Valerius Maximianus ( c. 260 - April or May 311 ) , commonly known as Galerius , was Roman Emperor from 305 to 311 .