Short answers, pulled from the story.
Anthrax released their extended play I'm the Man in 1987 which fused hip hop with heavy metal for the first time on a major label. Scott Ian of Anthrax later claimed that Rage Against the Machine invented the genre yet history shows earlier experiments.
The summer of 1999 saw rap metal reach its height of popularity according to the Port Huron Times-Herald and featured many artists associated with rap metal such as Kid Rock, Limp Bizkit, Rage Against the Machine and Reveille. The event included violence looting and fires happening at the festival which created lasting stigma for the genre.
Kid Rock released Devil Without a Cause behind Welcome 2 the Party on the 18th of August 1998 and the album sold 7 million copies before being certified 11 times platinum by the RIAA on the 17th of April 2003. Sales started slow until the Vans Warped Tour in Northampton Massachusetts stimulated regional interest.
SX-10 formed in 1996 by Sen Dog performs rap rock and rap metal. Cypress Hill incorporated direct heavy metal influences into their 2000 album Skull & Bones that record featured six tracks where rappers B-Real and Sen Dog were backed by Fear Factory members Christian Olde Wolbers and Dino Cazares.
Linkin Park released Hybrid Theory late in 2000 and it remains the best-selling debut album by any artist in the 21st century. The album was also the best-selling album in all genres in 2001.