persona non grata; unwelcome person; undesirable person
A formal, somewhat literary fixed expression used to describe someone who is not welcome in a particular group, place, or situation. Often carries a diplomatic or official tone.
He was considered a persona non grata in that country and was denied entry.
People who are undesirable to the company are often encouraged to take early retirement.
Literally 'uninvited guest', a similar construction but more specific to social situations. 好ましからざる人物 is more formal and can refer to any unwelcome person in any context.
A fixed phrase composed of 好ましからざる (the classical negative form of 好ましい, 'desirable') and 人物 ('person'). The use of the classical negative ざる gives the expression a formal, literary tone.