Aristonicus was a eunuch

Eunuch

A eunuch is a person born male most commonly castrated, typically early enough in his life for this change to have major hormonal consequences...

 of Ptolemy V Epiphanes

Ptolemy V Epiphanes

Ptolemy V Epiphanes , son of Ptolemy IV Philopator and Arsinoe III of Egypt, was the fifth ruler of the Ptolemaic dynasty. He became ruler at the age of five, and under a series of regents the kingdom was paralyzed.-Regency infighting:Ptolemy Epiphanes was only a small boy when his father, Ptolemy...

. He was brought up with the king from his early youth. Polybius

Polybius

Polybius , Greek ) was a Greek historian of the Hellenistic Period noted for his work, The Histories, which covered the period of 220–146 BC in detail. The work describes in part the rise of the Roman Republic and its gradual domination over Greece...

 speaks of him in terms of high praise, as a man of a generous and warlike disposition, and skilled in political transactions. In 185 BCE, when the king had to fight against some discontented Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

ians, Aristonicus went to Greece

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 and engaged a body of mercenaries there.

(Polybius

Polybius

Polybius , Greek ) was a Greek historian of the Hellenistic Period noted for his work, The Histories, which covered the period of 220–146 BC in detail. The work describes in part the rise of the Roman Republic and its gradual domination over Greece...

23.16-17.)