Rience is a mage of considerable skill who is sent after Ciri in the novel Blood of Elves. He is not as powerful as his master, Vilgefortz. In his quest to find her, he captures and tortures Dandelion to get information. If not for the extremely timely intervention of Yennefer, Dandelion might not have survived to continue his role as Geralt's frequent companion.
Yennefer's rescue of Dandelion leaves a permanent "impression" on Rience. While the mage does manage to escape with his life, the sorceress' final spell leaves the left side of his face permanently disfigured. Making him rather easier to track.
During the novel Time Of Contempt it is revealed that Geralt paid the legal consultation duo of Codringher and Fenn to gather all the research they could on Rience and on the person that Rience worked for. The information they gathered was considerable.
“ (…)My next information comes from Cintra. Rience served time in the dungeons there, during Queen Calanthe’s reign.” “(…)He didn’t stay long though, because someone bought him out after paying off the debts along with the interest (…) Whoever bought Rience out was a pro. And cared a great deal about preserving their anonymity.”
“(…)the brazen son of a bitch didn’t bother with secrecy: he continued to use the name ‘Rience’. And as Rience he began to search intensively for a certain party; to be precise a young, female party.”
“(…)It was a sorcerer who bought him out of that dungeon. You told me yourself – and Dandilion confirmed it – that Rience uses magic. Real magic, (…) So someone’s backing him, they’re equipping him with amulets and probably secretly training him.”“(…)So I repeat: Rience is in the service of a sorcerer and is operating so as not to draw the attention of other sorcerers to himself.”
Rience dies while pursuing Ciri across the frozen surface of Tarn Mira. The young witcher attacks Rience's party his own spell misfires and breaks the ice beneath his feet. Almost submerged in the freezing water he clutches the ice for his very life when Ciri skates through his fingers, severing them and leaving him to drown in the lake (in a cruelly ironic retaliation for his previous threaths abouth the things he would do to her "with these very fingers").