Early ATV's were amphibious - more like boats than motorcycles.
According to Wikipedia:
The term "ATV" was originally coined to refer to non-straddle ridden, typically six-wheeled, amphibious ATVs, such as the Jiger produced by the Jiger Corporation, the Amphicat produced by Mobility Unlimited Inc, and the Terra Tiger produced by the Allis-Chalmers Manufacturing Company in the mid-1960s and early 1970s. With the introduction of straddle-ridden ATVs, the term AATV was introduced to define the original amphibious ATV category.
The world's first production AATV is generally acknowledged to be the Jiger - developed by John Gower of Toronto and first marketed in 1960. A complete history of Jiger is published on a website devoted to these vehicles: Jiger.ca. The original model had 2 chain-saw type engines - each driving 3 wheels per side. The body was watertight - so the vehicle would float. Large tires with deep treads provided the ability to move the vehicle (very slowly) through the water. Jiger introduced a single-engine model in 1965 and started to ramp up production numbers. NASA expressed interest in the vehicle while exploring design options for the Lunar Rover.
Here's a quick video of a Jiger in action (note the transom for an outboard motor at the rear):
Jiger went bankrupt in 1968, but according to an article in the Toronto Star, it was not due to a lack of demand.
Meanwhile, in Orillia region, Hugh Thompson had been working on his own design for an AATV.
Orillia's OTACO was impressed with Hugh's design - and bought the rights to produce it. Through the late 1960s and early 1970s, OTACO marketed it as the Bazooo. Hugh Thompson and his family often appeared in the advertising.
You can see our Bazooo in action on this YouTube video:
The ATV market was literally redefined with the introduction of Honda's US90 ATC (All-Terrain-Cycle) in 1970. According to an article on "The History of ATVs" at ATVcourse.com :
... it was a hit. It was marketed and sold as a recreational vehicle and was famously portrayed in the James Bond movie Diamonds Are Forever, as well as in popular TV shows like Magnum P.I. and Hart to Hart. The three-wheeled US90 had a seven-horsepower engine and sold for $595 (USD) ...
Though ATVs were originally targeted towards sportsmen until the 70's gas crunch when customers began purchasing them as utility vehicles for agriculture and farming purposes. This was because ATVs cost exponentially less than a tractor, and guzzled only 8 percent of the fuel needed to feed a tractor.
OTACO discontinued production of the Bazooo in the early 1970s.