Short answers, pulled from the story.
Jordanes described the Heruli as a Germanic people driven from their Scandinavian settlements by Danes centuries before his sixth-century writing. Procopius recorded that Heruli noblemen migrated to Thule after their kingdom fell to Lombards, sending an embassy back to Scandinavia to find a king.
In 267, a Heruli fleet departed from the Sea of Azov and passed through the Bosphorus straits to take control of Byzantion and Chrysopolis. They subsequently raided Cyzicus and entered the Aegean Sea, troubling islands like Lemnos, Skyros, and Imbros before landing in the Peloponnese.
The Heruli consolidated a kingdom near the Morava river north of modern Vienna and Bratislava after Attila died in 453. This realm existed between 480 and 508 until King Rodulph lost it to the Lombards who had initially been under Herule hegemony.
Heruli forces could muster an army of 5,000 to 10,000 men while they held their kingdom near the Morava river. These numbers reflect the military capacity available before the kingdom fell to the Lombards around 508.
Dexippus gave a Greek etymology claiming the name derived from swamps helē of the Azov homeland. Modern scholars consider this etymology uncertain though thought Germanic, with some speculating connections to English word earl or runic inscriptions found in Scandinavia.