A person who represents a group, organization, or country in an official capacity.
He attended the meeting as a representative of the company.
Representatives from each country signed the treaty.
代表者 means a representative chosen to speak for a group or organization, while 代人 usually means someone substituting for one particular individual.
代表 can mean the concept, act, or person of representing, while 代表者 always refers specifically to the person who represents.
Compound of 代表 (representation) + 者 (person). The reading is on'yomi.