Billionaire Mark Cuban -- Paid $1,000 ... to Draw a Cat

Mark Cuban just raked in a $1,000 check for drawing a picture of two stick-figure cats kissing each other ... seriously.

It's not as random as it seems -- Mark is an "investor" on the reality show "Shark Tank" ... and recently sunk $25k into a company called, "I Want to Draw a Cat for You" -- a website that sells personalized cartoon cats for $9.95 a piece.

After he bankrolled the company, IWTDACFY jokingly posted an offer on the website that Cuban would personally sketch some cat art for $1,000 ... not thinking anyone would actually bite.

But they were wrong ... 'cause a short time later, a 24-year-old dude named David Switzer put up the cash ... and requested a kitty pic featuring himself and his girlfriend.

Mark tells TMZ ... although he has no prior cat-drawing experience, he's taking the job seriously ... and even reached out to the regular cat artist to get an idea of what the pic should look like (see below).