First appeared in New Teen Titans Annual #2 in 1983 and was created by Marv Wolfman and George Perez. The Harbinger assisted the Monitor in monitoring the DC Multiverse prior to Crisis on Infinite Earths.
This is going off the debut of comic book characters. In the cases of characters who were introduced in other media originally and added to the comics canon later along (ex: Harley Quinn) it'll go by actual debut year.
