| Frederick III | |
| Reign: | 23 March 1732 – 10 March 1772 |
| Succession: | Duke of Saxe-Gotha-Altenburg |
| Predecessor: | Frederick II |
| Successor: | Ernst II |
| Issue: | Frederick, Hereditary Prince of Saxe-Gotha-Altenburg Prince Ludwig Princess Fredericka Luise Ernst II Princess Sophie Prince August |
| House: | Saxe-Gotha-Altenburg |
| Father: | Frederick II, Duke of Saxe-Gotha-Altenburg |
| Mother: | Magdalene Augusta of Anhalt-Zerbst |
| Birth Date: | 14 April 1699 |
| Birth Place: | Gotha |
| Death Place: | Gotha |
Frederick III, Duke of Saxe-Gotha-Altenburg (14 April 1699 – 10 March 1772), was a duke of Saxe-Gotha-Altenburg.
He was born in Gotha, the eldest son of Frederick II, Duke of Saxe-Gotha-Altenburg and Magdalene Augusta of Anhalt-Zerbst.
After the death of his father, in 1732, Frederick III assumed the duchy of Saxe-Gotha-Altenburg.
In 1734 he began a flourishing soldier trade with the Emperor, to the Prince of Waldeck and to the King of Prussia, which put him into the position to create a tax in his own duchy. The duchy had to suffer for Frederick with difficulty in the Seven Years' War and he forced the duchy into a war with his neighbour, duke Anton Ulrich of Saxe-Meiningen (The "Wasunger War").
In Gotha on 17 September 1729, Frederick married Luise Dorothea of Saxe-Meiningen, his first cousin. They had nine children:
From 1748 to 1755 he was regent of the duchy of Saxe-Weimar-Eisenach on behalf of Ernst August II Konstantin. From 1750, he acted as regent alongside his kinsmen Franz Josias, Duke of Saxe-Coburg-Saalfeld. He died in Gotha, aged 72.
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