Anna Ripley

Dr. Anna Ripley was a follower of the Briarwoods. After the Briarwoods seized control of Whitestone, Percy attempted to kill Dr. Ripley in Stillben, but he was captured by her guards, tortured, and interrogated. Dr. Ripley began gathering intelligence about Percy's weapons and experimenting with firearm construction, losing a hand during one of her experiments. As an NPC, Dr. Ripley is played by Matthew Mercer.

Fascination with Percy
Ripley had a fascination with Percy's construction of his pepperbox firearm, "The List". While investigating her room at Whitestone Castle, Percy found many sketches of it drawn from eye-witness accounts.

She designed her own firearm, a pistol similar to Percy's pepperbox, but more technically refined and less aesthetically styled. It had only one barrel and a small, rotating, four-cylinder chamber. (When Percy began using Ripley's pistol later, he named it "Retort".)

Work for the Briarwoods
Dr. Ripley was working for the Briarwoods to create an acidic compound that would dissolve the white stone—for which Whitestone was named—in order to distill the stone into pure residuum, a powerful magical essence used in constructions like the Ziggurat.

When her work was completed, Ripley tried to leave, but the Briarwoods threw her into a dungeon under Whitestone Castle. Vox Machina found her there and begrudgingly let her out of her cell. She escaped the castle while Vox Machina fought Professor Anders.

Possible Activities After Whitestone
Returning to Vasselheim after liberating Whitestone, Percy learned that Victor, the black powder merchant, had done business with a nicely dressed lady several weeks prior, most likely Ripley.

Ripley fled from Vasselheim to Ank'Harel, as Vox Machina later discovered a crime scene there in which a firearm was used. Keyleth investigated her pistol, now in Percy's possession, and discovered a magical enchantment, which they learned Ripley was using to listen to them. Scrying on her, Keyleth discovered that Ripley did have Cabal's Ruin and was on a ship in the Ozmit Sea, most likely looking for Whisper, another Vestige of the Divergence.

Trivia

 * Dr. Ripley was the first character featured in Critical Role missing a hand, followed by Cerkonos, Tyriok Gadsworth, Shale, and Victor.