Botkin Yul-Erdene is the instructor for combat training classes. He was a former Shu Han mercenary who had fought multiple wars on every continent. He fought for anyone that could afford to pay him.
In Ruin and Rising, the Darkling presented a Dead Botkin, along with Ana Kuya and the three Grisha scouts on the tree in the front of the Kermazin Orphanage in a vision Alina was having. Alina yells at the Darkling that he hoped "he killed 20 of your Grisha, maybe even hundreds." The Darkling describes him as a very astonishing man.