Mathias is a Philistine olive oil merchant originally from Gath and the maternal uncle of Branan. At some point during Branan's childhood, Mathias evidently moved to Ashkelon and established a thriving business there until he and his family were run out of town because it became known that his sister gave birth to Samson's child. Mathias then relocated to Joppa and started a new life there.
Unfortunately, Sidon, looking to gain leverage against Branan, kidnaps Mathias and holds him hostage in Sidon's garrison in Joppa. After Branan musters a rescue party and frees his uncle from prison, Branan entrusts Mathias with a treasure chest full of plunder, charging him to return to Ashkelon and compensate the families of the thirty men Samson killed years ago. It is presumed that Branan and Mathias's gesture of peace worked and that Mathias and his family remained in Ashkelon from that point on.
Despite enduring persecution from his own people for being uncle to Samson's illegitimate son, Mathias nevertheless loves Branan and is the closest thing the boy has to a father figure. In the Adventures of Young Branan episode "Brigand's Lair," it is known that Mathias takes his young nephew on business trips where they discuss things like Branan and his mother's Jewish faith.
Even after Branan has grown up and become a man, he still enjoys visiting with Mathias and his three rambunctious boys at their home in Joppa. It is both telling and sad that Mathias is more of a father to his sister's son Branan than the "mighty" Samson ever was.