In Clash of the Titans (2010), this character,
is determined to convert people to worship Hades. Is he acting of his own free will or is he under Hades' influence?
His name is Prokopion and was played by Luke Treadaway in the 2010 version.
He was not being commanded by Hades, but he was influenced by him in the fact that he believed in him as others do Zeus. As stated by the Clash of the Titans Wiki:
Prokopion is the leader of the cult of Hades in Argos, and leads the cities' citizens to sacrificing Andromeda to the Kraken. Prokopion ultimately dies, when the petrified hand of the Kraken falls upon him.
He is simply acting as eccentric cult leaders do and of his own accord without direct influence from Hades.