A formidable force in the field, Conrad Marburg was employed by Halbech as recently as a year prior to the events of Alpha Protocol.
Studying his dossier shows that he's remarkably poor at reading people, assuming professionalism without any evidence of it. Regardless of his professional disposition, he is extremely pragmatic- he will sacrifice his men or retreat if it serves his ends. He is Halbech's pointman for their Rome operations due to his effectiveness.
Thorton can gain Marburg's respect by building up his dossier and giving only professional responses. If enough info is gained and enough respect is earned, Marburg can be convinced to betray Leland. Alternatively, gaining a poor enough reputation with Marburg with suave responses (and also building up his dossier) will allow Thorton to kill Marburg at the end of the Rome quest line.