NOTE: As mentioned elsewhere, DC comics has had many characters that went by the name "Manhunter". The first costumed Manhunter from DC originally appeared in Adventure Comics #73 (April 1942).
But prior to that, DC had a feature called "Paul Kirk, Manhunter" that began in Adventure Comics #58 (January 1941).

That feature ran through issue #72 (March 1942).

The following issue (Adventure Comics #73, cover-dated April 1942) saw the introduction of a costumed character named "Manhunter":

but for some reason, he was referred to as "Rick Nelson" for this episode.
When the feature returned for issue #74, the character was now named "Paul Kirk", but there did not seem to be any connection to the previous "Paul Kirk, Manhunter" feature that had previously ran in that title.

There's still more to talk about regarding all the appearances of Paul Kirk, but we'll save that for later.
In the meantime, from Who's Who: The Definitive Directory of the DC Universe Vol. XIV (April 1986):


NOTE: This thread is specifically for the Paul Kirk version of Manhunter. If people wish to discuss other versions, please look for (or create yourself if they don't already exist) separate threads regarding those other versions.