Klaus was a servant of Herbert Montague's ancestors.
One hundred years after Klaus' death, Herbert's home was visited by strange phenomena. He enlisted the help of the Seventh Doctor, who found the cause of the disturbances to be Klaus, who had died protecting the Doctor and Herbert's ancestors. Klaus was supposed to become a companion of the Doctor. The Doctor gave him the memories of the adventures he should have had, and he left the Montague family in peace. (PROSE: Perfect Present)