Pantaleon (Ancient Greek: Πανταλέων, Pantaléōn) was a Greek king who reigned some time between 190 and 180 BC in Bactria and India. He was a younger contemporary or successor of the Greco-Bactrian king Demetrius, and is sometimes believed to have been his brother and/or subking.
The scarcity of his coinage indicates a short reign. Known evidence suggests that he was replaced by his (probable) brother or son Agathocles, by whom he was commemorated on a "pedigree" coin.
The Greco-Bactrian Kingdom (Greek: Βασιλεία τῆς Βακτριανῆς, romanized: Basileía tês Baktrianês, lit. 'Kingdom of Bactria') was a Greek kingdom during the Hellenistic period located in Central Asia and Afghanistan. The kingdom was founded by the Seleucid satrap Diodotus I Soter in about 256 BC, and continued to dominate Central Asia until its fall around 120 BC. At its peak the kingdom consisted of present-day Afghanistan, Tajikistan, Uzbekistan and Turkmenistan, and for a short time, small parts of Kazakhstan, Pakistan, India and Iran. An extension further east, with military campaigns and settlements, may have reached the borders of the Qin State in China by about 230 BC.
A Greek population was already present in Bactria by the 5th century BC. Alexander the Great had conquered the region by 327 BC, founding many cities, most of them named Alexandria, and further settling Macedonians and other Greeks. After the death of Alexander, control of Bactria passed on to his general Seleucus I Nicator. The fertility and the prosperity of the region led to the creation of the Greco-Bactrian kingdom under Diodotus by the early 3rd century BC, as a successor state of the Seleucid Empire. The Bactrian Greeks grew increasingly more powerful and invaded north-western India between 190 and 180 BC under king Demetrius, the son of Euthydemus. This invasion led to the creation of the Indo-Greek kingdom, which in turn was a successor to the Greco-Bactrian kingdom, and was subsequently ruled by the kings Pantaleon and Apollodotus I. Historical records indicate that many rich and prosperous cities were present in the kingdom, but only a few of them have been excavated, such as Ai-Khanoum and Bactra. The city of Ai-Khanoum, in north-eastern Afghanistan, had all the hallmarks of a true Hellenistic city with a Greek theater, gymnasium and some houses with colonnaded courtyards.