Xander Thiessan is a character that appears in Tom Clancy's Rainbow Six: Lone Wolf.
Xander Thiessan is a convicted terrorists from Solhiea, Norway. He along with his brother were part of a terrorist organization that was illegally shipping weapons into Russia. Both eventually left the organization for unknown reasons. Xander grew paranoid after leaving the group and began to suspect that they were monitoring him. On January 25th, 2001, Xander contacted Rainbow about the weapon imports and agreed to divulge more information once he was safe and in custody. Domingo Chavez was dispatched Solhiea under the cover of night to validate Xander's information.
Once confirmed, Chavez told Xander to rendezvous with him on the other side of town the next morning to avoid suspicion. Unfortunately, the terrorist organization learned of Xander's betrayal and kidnapped him before Chavez could reach the rendezvous site. Xander was then taken into a nearby cave system that the terrorists had been using for weapon smuggling. Chavez was able to dispatch the terrorists and rescue Xander. Xander then informed Chavez that he would not reveal any more information about the group until he was certain his brother was safe. On January 28th, Chavez traveled to a small village west of Solhiea and rescued Xander's brother who had been taken hostage by the terrorists. With his brother safe, Xander revealed the terrorist's regional headquarters to be located in farmhouse in a valley several miles east from Solhiea. On January 30th, Chavez infiltrated the farmhouse and shutdown the smuggling operation.
As noted by Kevin Sweeney, Xander is an intelligent but arrogant man. He is the kind of person who despises people who he feels are not as his equal. This and Xander's history of being deceitful led to Sweeney being suspicious of him. The paranoia of his former group monitoring him made Xander fearful for his safety and ultimately led him to contact Rainbow.