Metallus is the chronicler of the tale recounted in "The Island of Pirate's Doom" which is serialized in six parts in Savage Sword of Conan issues 73, 74, 76-79.
In this story he encounters Valeria of the Red Brotherhood on an unnamed island in the Wsetern Sea. He joins her in evading the rest of her angry crew who desire to kill her.
Metallus proves to be a very capable swordsman able to hold his own and more against seasoned pirates. Eventually he begins to fall for Valeria as he sees that she is indeed a good person despite being an infamous pirate.