The top known title in Sea of Thieves is Pirate Legend. In order to achieve that title, you must reach level 50 reputation for each of the three Trading Companies.
Spoilers for what happens once you attain Pirate Legend follow.
First, reach level 50 reputation across all three Trading Companies. Simple, right? Once you’ve accomplished that collect your title by wearing all of your newly unlocked Pirate Legend gear with the vanity chest.
Pirate Legend Prod1gyX’s gear
Congratulations! You’re now an official Pirate Legend. But there’s more to it than just the gear.
To fully reap the benefits of being a Pirate Legend, visit a tavern and talk to the Mysterious Stranger. You’ll receive the following riddle and a new song to play:
Through many voyages upon the sea, you searched to find the legends key.
Now one last step to pass the Tests, to find where Athena’s Fortune Rests.
Take this tune and make a sound, the secret lies near in the ground
Stay in the tavern and walk toward the wheel on the wall by the broken staircase. Play the special song you received with this riddle and the floor will open.
Walk down the staircase to reach the fabled Athena’s Fortune. In this special area you’ll find Pirate Legends hanging out, playing music, and drinking glowing grog that you can drink too. Players that haven’t earned the Pirate Legend title can enter with you, but they can’t buy anything in this area.
Now that you have access to Athena’s Fortune, you can buy special Pirate Legend ghost gear as you complete voyages and earn reputation for Athena’s Fortune.
There were no ship customization parts in Athena’s Fortune at the moment, but Liz at the shipwright shop says the following line when asked if there’s any new stock:
“Coming soon to a shipwright near you, a delightful range of ship accessories for the discerning pirate legend.”
Athena’s Fortune voyages combine quests from the other three Trading Companies. The first voyage shown by streamer Prod1gyX had eight parts. Each voyage cost 250 coins and can be purchased from the Pirate Lord.