Bolens started producing 2-wheel walk behind garden tractors in the 1920's and continued building them up into the 50's.
They came out with the 4-wheel Ridemaster garden tractor is 1948.
The Ridemaster was built like a walk behind tractor with a permanently attached sulky and the implements mounted between the front and rear wheels.
In 1958 they came out with the Ride-A-Matic garden tractor.
This was designed like a regular 4-wheel tractor with the implements attached behind it.