In exchange for an Ancient Coin, Isidro helped set up Flameheart Jr with a ship, a crew, and led him to the Sea of Thieves. He stayed in the company of Flameheart Jr until the fateful meeting with Cap'n, where it is unknown if he is still alive.
It was at Isidro's behest that Flameheart Jr met with the strange old woman who gave him the map.
Not much is known about Isidro's life before his meeting with Flameheart Jr. He appears to have sailed the Sea of Thieves before as he has knowledge of the place.
Isidro's name appears as one of the options for Replace Gamertag as 'Trading Isidro'.