Hired by Kristen DiMera to steal Theresa Donovan's embryo (November 2014)
Hired Clint to spy on Theresa (January - February 2015)
Dr. Mandrake is a fertility specialist who works for the DiMera family. Specifically, Kristen DiMera hired him to steal Theresa Donovan's embryo and implant it in her. Theresa was pregnant with Brady's baby and Kristen wanted the child for herself.
Part of Dr. Mandrake's role was also to ensure that Theresa would not remember the crime. So, he drugged her before the procedure. And then as a precaution, he sent a henchman, Clint, to Salem to check in on Theresa and make sure that she had no memory of the night her baby was stolen.