You can check out this related thread for some discussion. https://www.reddit.com/r/AskHistorians/comments/18zhmq/why_is_john_hanson_not_recognized_as_the_first/?

To give you a quick answer though, from 1781 until 1788 the U.S. was governed by the Articles of Confederation. There was no strong executive in this system and only one house of Congress.

That Congress was presided over by an elected congressman, but their role was much more like the current Vice Presidential role of president of the Senate than to the current U.S. President.

I know Wikipedia isn't a preferred source but it's basic info on this is solid and it has a list of the men who served this role here: https://en.m.wikipedia.org/wiki/Articles_of_Confederation