Herennius Etruscus (227-251) was the son of Emperor Decius Trajan and older brother of future Emperor Hostilian. Herennius was born in Pannonia during one of his father's military postings. He joined the army to fight alongside his father, and followed his father in his rebellion against Emperor Philip. Herennius became heir to the throne in 249.

When the Gothic tribes began raiding across the Danube frontier, Herennius' father raised him to the rank of co-emperor, and together they embarked on a campaign against the Goths, while Hostilian remained in Rome. It was during the fateful Battle of Abrittus that Herennius died in battle, struck by an enemy arrow.