Gallienus (Latin: Publius Licinius Egnatius Gallienus Augustus; c. 218 – 268) was Roman Emperor with his father Valerian from 253 to 260, and alone from 260 to 268. He took control of the Empire at a time when it was undergoing great crisis. His record in dealing with those crises is mixed, as he won a number of military victories but was unable to keep much of his realm from seceding.

Based on the testimony of John Malalas and the Epitome de Caesaribus that Gallienus was about 50 years old at the time of his death, it is generally considered he was born around 218, son of Valerian and Mariniana, a woman possibly of senatorial rank and possibly a daughter of Egnatius Victor Marinianus, and brother of Valerianus Minor. Inscriptions on coins connect him with Falerii in Etruria and this may well have been his birthplace; it has yielded many inscriptions relating to his mother's family, the Egnatii.

He married to Cornelia Salonina about ten years before his accession to the throne. She was the mother of three princes, Valerian II (who died in 258), Saloninus (who, after becoming co-emperor, died in 260 by the hand of his general Postumus), and Marinianus (killed in 268, shortly after his father was assassinated).

Trebonianus Gallus (Latin: Gaius Vibius Afinius Trebonianus Gallus Augustus; 206 – August 253), also known as Gallus, was Roman Emperor from 251 to 253, in a joint rule with his son Volusianus.

Gallus was born in Italy, in a family with respected ancestry of Etruscan senatorial background. He had two children in his marriage with Afinia Gemina Baebiana: Gaius Vibius Volusianus, later Emperor, and a daughter, Vibia Galla. His early career was a typical cursus honorum, with several appointments, both political and military. He was suffect consul and in 250 was nominated governor of the Roman province of Moesia Superior, an appointment that showed the confidence of Emperor Trajan Decius in him. In Moesia, Gallus was a key figure in repelling the frequent invasion attacks by the Gothic tribes of the Danube and became popular with the army, catered to during his brief Imperial rule by his official image: military haircut, gladiatorial physique, intimidating stance (illustration, left).

In June 251, Decius and his co-emperor and son Herennius Etruscus died in the Battle of Abrittus, at the hands of the Goths they were supposed to punish for raids into the empire. According to rumours supported by Dexippus (a contemporary Greek historian) and the Thirteenth Sibylline Oracle, Decius' failure was largely owing to Gallus who had conspired with the invaders. In any case, when the army heard the news, the soldiers proclaimed Gallus emperor, despite Hostilian, Decius' surviving son, ascending the imperial throne in Rome. This action of the army, and the fact that Gallus seems to have been on good terms with Decius' family, makes Dexippus' allegation improbable. Gallus did not back down from his intention to become emperor, but accepted Hostilian as co-emperor, perhaps to avoid the damage of another civil war.