And on Friday, March 15, they closed out the whole thing in style by doing yet another installment in their epic 'History of Rap' series.

Slow down, guys. It's only the second night and you're already making us giddy.

But in his Nov. 8 appearance on 'Late Night With Jimmy Fallon,' he was kind of adorable -- even to us -- when he gamely climbed into a big wooden tub and had a water fight with Fallon.

After urging Congress to stop the doubling of interest rates on Stafford Student Loans earlier in the day, the President appeared on the late night show to sing a song with Jimmy about why he thinks it's important. Check out the video after the jump!

But on last night’s ‘Late Night,’ Jimmy Fallon decided to have some fun with the gossip by reworking the lyrics to Bieber’s biggest hit. ‘Baby.’

The last time Justin Timberlake visited Jimmy Fallon on Late Night, the two performed a hilarious medley of old school hip-hop songs in "History of Rap". The video of that performance went viral almost immediately. Timberlake and Fallon brought the routine back last night, much to the delight of the studio audience and those of us watching at home. Fallon and Timberlake picked up where they left off (in the late 80's) and covered the past twenty years of rap with parts of hits by Public Enemy, N.W.A., Salt-n-Pepa, Cypress Hill, DMX, Outkast, 50 Cent, Lil Wayne and Rick Ross. The sing along version of Biz Markie's "Just A Friend" is amazing, and the audience was really into it. But, current major rap icons like Eminem, Jay-Z, Snoop Dogg, Kanye West, and the Beastie Boys weren't included. Check out the video after the jump!

On Friday night's episode of 'Late Night With Jimmy Fallon,' funnyman Stephen Colbert made a special musical appearance, in which he fittingly performed Rebecca Black's viral Internet song 'Friday' alongside house band The Roots.