The Curator was the leader of the Quintesson race.
When the Ark appeared over Quintessa, Optimus Prime made contact with the Curator. Ground-Bridgeing to the surface, with a few of his troops, Optimus engaged in talks with the Curator.
The two compared the history of their two peoples. The Curator was amazed to learn that Optimus was a Prime and that a Cybertronian would even speak to him. He explained how the Quintessons had long since abandoned their violent ways and were a peaceful race. Hearing how the Cybertronians were engaged in a war that destroyed their planet. The Curator offered to mediate peace talks between Optimus and Megatron, claiming it was the least he could do after his race's crimes against Cybertron.
The Curator "invited" Megatron and Starscream to Quintessa, through use of a tractor beam, when the Nemesis eventually arrived. He spoke to both Optimus and Megatron and listened to their arguments. However, unknwon to him Megatron had ordered Starscream to seize the Engergon and Optimus ordered Kup to defend it. The result was a massive firefight and explosion that ravaged the Quintesson city.
When he left Quintessa, Optimus hoped the Curator had survived, hoped he could one day renew peace talks with the Quintessons and hoped this would not have destroyed any chance of peace with the Quintessons.
The Curator's fate is unknown.
The Curator was a kind individual. He was very dedictaed to peace and knowledge and tried to help wherever he could. However, his life left him unprepared for Megatron's treachery which eventually destroyed his city.
The Curator got along very well with Optimus Prime, who compared him to Alpha Trion.