Who is Gullberg from The Girl Who Kicked the Hornet's Nest and what is their importance?

Evert Gullberg is the former Senior Administrative Officer at the Security Police. He also served as the original head of the Special Section (SSA) in Stockholm, Sweden. Gullberg is brought out of retirement in order to deal with Zalachenko. He eventually catches up with Zalachenko in the hospital before killing him and taking his own life.