Geralt of Rivia helped Emhyr var Emreis (using the alias Duny) from him being killed and lifting his curse. Duny filled with gratitude was willing to give the Witcher any reward he asked. Geralt asked for the Law of Surprise, an oath binding magical law that has unexpected results. Turns out Dunys bride Pavette was pregnant when this oath was made forever intertwining the fate of the baby; Princess Cirilla Fiona Elen Riannon, and Geralt forever.
The Order of the Witchers, now mostly completely wiped out, had several schools of learning that were each proficient in their own art. The School of the Wolf was one of the most recognised of these schools as its members gained the reputation of professional and reliable monster slayers. Geralt dons this set of armor from the School of the Wolf, his own school of study, with layered jackets and reinforced metal studs and rivets.