noun

a person who is appointed to undertake the duties of a superior in the superior’s absence.

his deputy has been largely running the business for the past year

second in command,second,number two,subordinate,junior,auxiliary,adjutant,lieutenant,subaltern,assistant,personal assistant,PA,aide,helper,right-hand man,henchman,underling,substitute,stand-in,fill-in,relief,understudy,supply,representative,surrogate,proxy,delegate,agent,spokesperson,ambassador,legate,depute,locum tenens,vice,man/girl Friday,sidekick,locum,temp,acting,reserve,caretaker,temporary,short-term,provisional,stopgap,pro tempore,ad interim,second-string,pinch-hitting,expediential