Gullivarrr is Gulliver, but wearing a pirate costume and talking in pirate puns. He washes up on shore, much like regular Gulliver, and needs help getting back to his ship. Has was added in the 1.3.0 update as a random daily visitor.
If you return his communicator, he will mail you a reward the following day.
Since Gullivarrr is just Gulliver in a different outfit, helping him counts towards the achievement "Gulliver's Trevails".