Ernest the Iron (born 1377 in Bruck an der Mur; died June 10, 1424 in the same place) was a Duke of Austria from the Habsburg dynasty, and as a member of the Leopoldinian Line the ruler of Styria, Carinthia and Carniola.

After the death of his father Leopold III in the Battle of Sempach in 1386, he stood under the guardianship of Albert III, and in 1401 accompagnied the German King Ruprecht III auf his campaign in Italy. In the separation agreement of 1406, Ernest received Styria, Carinthia and Carniola, and jointly with his brother Leopold, held the guardianship over young Albert V. This resulted in a civil law in 1407, which could only be ended in May of 1409. In 1414, he was the last Duke be inthronized according to the traditional rite in Carinthia, and from that time on called himself Archduke. He was the first Habsburg to actually use this title, which had been invented by Rudolf IV.

He continously lived in strife with Emperor Sigismund from 1412 onwards. When his brother Fredrick was banned by the Emperor in 1417, Ernest first attempted to gain control over Frederick's territories himself, buth then came to an agreement with him and successfully defended the Tyrol against the Emperor's pretensions. As the regent of Inner Austria and the founder of the older Styrian Line of the Habsburg family, which, by his son Duke Frederick V survived the Albertinian-Austrian and the Tyrolean Lines, he became the ancestor of all later Habsburg Emperors. Other children include Albert

His first spouse was Margaret, Princess of Pomorania , and the second was Cymburgis of Masovia, who was his equal in vitality and with whom he had nine children. Ernest's grave is in the Cistercian monastery of Rein . His nickname the Iron only came into use after his death.