Who is the only president to have held a patent?

The answer is: Abraham Lincoln. Back in 1849, well before he stepped into office, President Lincoln received approval for a patent on a device intended for “buoying vessels over shoals.” After getting stranded in the Mississippi River twice while working as a ferryman, the idea was to have some kind of inflatables around a boat that would allow it to be slightly raised and get over obstacles.It was never produced or put into action, but it’s still quite the distinguishment for an already quite distinguished president. Source