Severus Alexander (Latin: Marcus Aurelius Severus Alexander Augustus; 1 October 208 – 18 March 235) is Roman Emperor from 222 to 235.

Alexander is the last emperor of the Severan dynasty.

He succeeds his cousin Elagabalus upon the latter's assassination in 222, and is ultimately assassinated himself, marking the epoch event for the Crisis of the Third Century — nearly fifty years of civil wars, foreign invasion, and collapse of the monetary economy.

Alexander is the heir apparent to his cousin, the eighteen-year-old Emperor who had been murdered along with his mother by his own guards, who, as a mark of contempt, had their remains cast into the Tiber river.

He and his cousin are both grandsons of the influential and powerful Julia Maesa, who had arranged for Elagabalus' acclamation as emperor by the famed Third Gallic Legion.

It is the rumor of Alexander's death that triggers the assassination of Elagabalus and his mother.

As emperor, Alexander's peacetime reign is prosperous.

In military conflict against the rising Sassanid Empire, there are mixed accounts, though the Sassanid threat was checked; however, when campaigning against Germanic tribes of Germania, Alexander apparently alienates his legions by engaging in diplomacy and bribery, and they assassinate him.