Conversation so far:
When did the Hellenistic period take place?
4th century BC.
Where were the Illyrians located?
Greco-Roman historiography.
Did the Illyrians have a Ruler/King/President?
The Illyrians formed several kingdoms in the central Balkans, and the first known Illyrian king was Bardyllis.

Question: Were they peaceful or warlike?
Self-contained rewrite: Were the Illyrians peaceful or warlike during the Hellenistic period?