It's easy to take for granted that ATVs designed from the factory to carry a passenger exist but this wasn't always the case.

Do you know who started the trend and when? You will after reading this piece:

A Brief History of 2-Up ATVs - ATVConnection.com

 

Good list but you've left out one that I see often enough on the trails. The Polaris Sportsman X2. Had one for many years before the Can-Am. Was a great all around quad and Mrs. Moose was comfortable enough on the flip up seat.

2017 Sportsman X2 570 ATV | Polaris

Polaris now even has a 6x6 that is quad width and can carry a passenger too.