Date: March 14, 2019 12:45PM
I do now, thanks to Google: http://www.withoutend.org/jason-mack/
In the comments section, someone refers to a FAIR report regarding the first vision(s), in which Jason Mack is mentioned, along with Joseph Smith, Sr. The two men were brothers-in-law.
From my limited perspective, Jason Mack is just another tool to be used by both sides, each for their own purpose.