Before Roger Federer vs. Rafael Nadal, there was Bjorn Borg vs. John McEnroe.

The two tennis stars had an intense rivalry during the ’70s and ’80′s are the subject of HBO’s latest documentary, McEnroe/Borg: Fire & Ice.

The 60-minute special documents the back story of both tennis stars – - from Borg’s youth of growing up in Sweeden to McEnroe and how he developed into the pretentious phenom that fans loved to hate.

At the end of the day, despite their intense rivalry, the two not only shared a deep respect for each other but would eventually form a close friendship.

“The least I could do was to try a little harder when I was playing him,” McEnroe says in the documentary. “I had to be on my best behavior, plus I respected him.”

In order to fully appreciate this documentary, you need to be of a certain age and lived through the McEnroe-Borg rivalry. For the 20-somethings like myself, it might be hard to grasp why this rivalry trumps Federer-Nadal or Andre Agassi-Pete Sampras.

McEnroe/Borg: Fire & Ice airs Saturday night at 10 p.m. ET on HBO.