While Brown and Peterson were regularly playing duets, Brown suggested that they extend the formation to a trio in 1951. After a short try with Charlie Smith on drums, they soon moved to a piano/bass/guitar line-up, working with either Barney Kessel or Irving Ashby during the first couple of years. Kessel left at the end of the season, and Brown suggested Herb Ellis as a replacement. This line-up is what is usually referred to as The Peterson Trio, and will last up to 1958.
After Ellis retirement, Brown and Peterson couldn't replace him and decided to change the trio structure with the inclusion of drummer Ed Thigpen, a new line-up that would again produce some massive amount of stellar material (including the grueling year 1962).
In 1965, both Brown and Thigpen retired, putting an end to the specific alchemy that defined the classic Peterson trio.
Though there were later on a number of other trio sessions led by Peterson (including with Joe Pass, NHØP, Bobby Durham, Louis Hayes, Sam Jones, Jake Hannon), they do not belong to this group and should be filled under "Oscar Peterson".
Note that a late 80s reunion would reunite Ellis/Brown/Peterson for a serie of Blue Note lives.