I enjoy the concept you mentioned regarding the goblin being "gifted" to a noble by adventurers who killed its tribe. Good excuse for the goblin to have a chip on its shoulder.
I actually have the backstory played out...the goblin found the normal day-to-day activity of his tribe raiding / pillaging to be mundane.
Then after one particular raid, they bring the survivors in for the usual slave labor...and one of the survivors happens to be a bard (in this case, the bard subclass will mimic whoever the bard is).
The goblin finds the bard's instrument and books among the loot, and they pique his curiosity. He visits the bard in his cell, and the bard indulges the goblins curiosity by reading from the tome, which contains tales of various adventures. The bard also teaches the goblin the basics of playing the musical instrument. The goblin immediately becomes fixated on the stories, having never heard of anything like them, and becomes entranced by the music. The goblin & the bard develop a shaky friendship in secret, with the bard instructing the goblin in the bardic arts, teaching him to read from the book. Doing so unlocks the innate magical power within the goblin, a rare occurrence among goblins, which they refer to as "booyahg" in their own tongue.
Upon his tribe discovering this power, they intend for the goblin to use the magic to expand their territory. Magic is, after all, a powerful weapon. But with the goblin's increasing uncertainty regarding his own race and their violent tendencies, the goblin instead breaks the bard out from his cell, and the two escape in the middle of the night.
The goblin has a fervent desire to understand art and magic, and the strange world his people once terrorized. Obviously, he travels under cover, with his bard mentor providing some instruction how to safely move among the other races.
He's a bit rough around the edges, but he's got a good heart. His wish is to prove that he isn't a threat, while being accepted as an adventurer and artist like his mentor. He learns the written word, and practices writing down the stories he experiences while adventuring. In combat, he recites battle chants taught to him by his mentor.
He is not, however, a warrior...at best, he's a scrapper: he'll dive in for an ambush, and then run like hell.