I was watching an old episode of the Monkees from 1966. In the theme song they are riding what looks like at first glance to be skatebikes.
From “Monkee vs. Machine” (Sep 26, 1966)
I found a page on The Cabe: I’m Looking For Information About “The Monkees” Unicycles
The modified unicycle was made by Mattel for the show. US Patent 3,392,991, issued in July 16, 1968 and expired in July 16, 1985 explains the design. This is interesting in that it predates the June 18, 1981 patent by Yves Garel (France) files the velocipede patent by13 years.
The bike uses a unicycle wheel with fixed cranks. No brakes are necessary. The back wheels stabilize and help prevent falling off backwards. I was impressed how well they rode.