He would have been his close associate had he not been disloyal.

Answer: Option C

Employee : a person employed for wages or salary, especially at non-executive level.
Competitor : a person who takes part in a sporting contest.
Colleague : a person with whom one works in a profession or business.
Executive : relating to or having the power to put plans or actions into effect.
Associate : a partner or companion in business or at work.

Synonym of Associate is Colleague