IN: Which person is he?
Ryan won the presidency against Tom because he was not fit for office.
OUT: Tom

IN: Which person is they?
Western Digital may disappoint their shareholders this season since they have slowed down production in their Thailand factories due to flooding.
OUT: Western Digital

IN: Which person is they?
Western Digital may disappoint their shareholders this season, but they will probably tough out the momentary losses and remain shareholders.
OUT: their shareholders

IN: Which person is he?
The policeman finally caught the criminal, because he used pepper spray and handcuffs.
OUT:
The policeman