Complex sentence: Reichsgraf Otto Magnus von Stackelberg (1736--1800) was a diplomat of the Russian Empire, an envoy in Madrid from 1767 to 1771, ambassador in the Polish-Lithuanian Commonwealth from 1772 to 1790 and in Sweden from 1791 to 1793.
Split into simpler sentences: Reichsgraf Otto Magnus von Stackelberg (1736--1800) was a diplomat of the Russian Empire. He served as an envoy in Madrid from 1767 to 1771, ambassador in the Polish-Lithuanian Commonwealth from 1772 to 1790 and in Sweden from 1791 to 1793.