The Rock and Triple H intially started their feud back in 1998 where Triple H took over D-Generation X and The Rock took over the Nation of Domination.
The Rock and Triple H first met on Raw in June of 1998 in a King Of The Ring Qualifying match. With help from the Nation of Domination, The Rock defeated Triple H to advance to the King Of The Ring Semi-Finals. The Rock however, would not win the King Of The Ring title that year.
A month later at Fully Loaded in July, Triple H met The Rock for the Intercontinental Championship in a Best two-out-of-three Falls Match. Due to a 30 minute time limit, that match ended in a draw because the expiration of the 30 minutes.
The Rock and Triple H would settle the score for the Intercontinental Championship a month later at Summerslam in Madison Square Garden. The match would be a Ladder Match.
After a hellacious match, Triple H was able climb the ladder to the freedom land to become the new Intercontinental Champion.
Triple H and The Rock would take a year off from battling each other. Both The Rock and Triple H would become multiple WWE Champions in 1999.
In 2000, The Rock and Triple H renewed their rivalry at Wrestlemania. Vince McMahon would screw The Rock from becoming the WWE Champion once again.
However, at Backlash with help from Stone Cold Steve Austin, The Rock defeated Triple H and became the new WWE Champion.
At Judgment Day in 2000, Triple H and The Rock met in the only second ever modern era 60 Minute Iron Man Match for the WWE Championship. Triple H's good buddy Shawn Michaels was the special referee in the match.
That match became instantly one of The Rock's and Triple H's best matches throughout their careers.
With an interference from the returning Undertaker, Triple H defeated The Rock to become the new WWE Champion.