This article contains plot details from the latest book.
“I like being a Vacker—or I did until all of this happened. I know you're probably going to think I'm a jerk for admitting that, but... I like knowing I'm part of a huge legacy—and not whatever creepy legacy Alvar was talking about that has Biana all freaked out.”
—Fitz, in Flashback
First mentioned by Alvar Vacker at the end of Book 4: Neverseen, The Vacker Legacy is still mostly unknown. Part of it seems to be related to the Troll Hive at Everglen discovered in Book 7: Flashback or Alvar's involvement with the Neverseen. Alvar has told Biana that she will someday understand what the Vacker Legacy is, but not Fitz.
"You'll understand, someday, when you see the Vacker legacy for what it is."
It can also be understood as the Vacker's less mysterious legacy: Fallon Vacker was an original member of the three-elf council, meaning that they're one of the most ancient and well-known Elvin families.