Here is my two cents:
Jim Heusinger, founder of Berea Hardwoods was one of the first to offer kit pens. You can read his interesting story
HERE The Ohio Chapter visited Berea for a meeting once and Jim gave us the whole history of penmaking and it was fascinating. I wish I had thought to take a video.
Hut Products and Craft Supplies were also offering pen kits in the late 80's early 90's
@ed4copies has a great deal of pen business history in his head. I believe he gave a talk at an MPG. The link in JT's post above has some more info from Ed.
As far as people in penmaking goes, you can't find anyone more influential than Dick Sing. Check out
this video
Russ Fairfield was also an icon in the penturning world. I learned to turn reading Dick's and Russ's books.
IAP was started by Scott Greaves and me in 2004 with lots of help from many people. If I started to list the people who have been very influential in the history of IAP, I'd be here all night.
I just asked Gemini "who was the first company to offer pen kits" and she says:
I couldn't find a definitive answer on the first company to offer pen kits. However, Berea Hardwoods is often mentioned as a pioneer in the early days of pen kits. They established standards like the "A" mandrel size and played a significant role in the development of the pen kit industry. You might find more specific information on the history of pen kits by reaching out to the International Association of Penturners or researching historical records from woodturning and crafting communities.