"The Real Slim Shady" was written a few hours before the album was due!

The record company wanted Eminem to have a track to introduce the rappers third album "The Marshal Mathers LP," much in the same way that the song "My Name Is" introduced his previous album "The Slim Shady LP." 

When the record company asked this, Eminem got to work and wrote it with only a few hours before the final cut of the LP was due to the record company! The song was released as the first single and became one of his biggest hits. It was his first song to hit the top of the charts in the UK and peaked at #4 in the Billboard top 100. 

(Source)