Anselm was a Fallen Knight who died shortly before the events of Hearts of Stone expansion for The Witcher 3: Wild Hunt. His orders from Grand Master Ulrich were that he travel to Novigrad to resupply and sell the latest batch of fisstech. Customers however betrayed him at the deal and instead killed the knights under Anselm's command leaving him the sole survivor. They would also kill him, but first they needed the key to the chest containing the fisstech. It turned out that they could not find the aforementioned key because Anselm had slipped it into his butt.
Even though his captors were later killed by drowners, he could not escape because they locked him up in the cellar of a hut, the place of the meeting. After three days he had nothing left, no food or drink, not even hope so he decided to write a letter before dying.