Dave Grohl was, for four years, the drummer of Nirvana. Grohl started with the group when he was just 21 years old, after they had released Bleach (see TMFW 32 for the story of album cover subject Jason Everman) and just before the band signed with DGC records (see TMFW 42 for the story of David Geffen's early-career subterfuge). Grohl was with the band for the recording, release, and subsequent youth culture freak-out over Nevermind, and stayed with them until the band's break-up after Kurt Cobain's death.
But Nirvana was, by and large, Kurt Cobain's band. Though Grohl was a songwriter, he mostly kept his work to himself while he was a part of Nirvana. He had only a few songwriting credits on the group's records, and only one Nirvana song was written by him alone (that would be "Marigold," the B-side to the "Heart-Shaped Box" single.)
To scratch his songwriting itch while he was with Nirvana, Grohl made an album in which he wrote all of the songs and played all of the instruments. Recorded over two days in December 1990 and July 1991 and titled Pocketwatch, Grohl released the record on a limited-run cassette under the pseudonym "Late!" You can listen to the whole album on YouTube; it's decidedly lo-fi and heavily instrumental but not bad at all for two days' work.
Grohl's release as Late! is an interesting story, but the larger True Music Fact is that later in his career, Grohl repeated the "write all the songs and play all the instruments" arrangement. After struggling to play music following Kurt Cobain's death, Grohl decided that he would work on a solo project as "some sort of cathartic therapy, to go out and record these songs that I'd written by myself." He reserved six days all alone (but for the recording staff) at a Seattle recording studio, and emerged with a record. Calling himself "Foo Fighters," he dubbed the songs to cassette and gave copies to friends. The cassette sparked interest from major labels, and it was later professionally mastered and distributed by Capitol Records as Foo Fighters, the "band's" self-titled debut release. It wasn't until he set out to tour - it's a little difficult to play all of the instruments at a live show - that Grohl recruited other members to join the group.
The band that started as Dave Grohl's "cathartic therapy" solo project has gone on to release seven albums and sell over 11 million records. Six of the seven records charted in the top 10, four reached the top five, and the latest record reached number 1. Not too shabby.
BONUS FACT: Among his fans, Dave Grohl is revered for being the "nicest guy in rock and roll" - see this Buzzfeed list of "26 Things That Scientifically Prove That Dave Grohl Is the Coolest Dude in Music," this Spin article listing "10 Reasons Why Dave Grohl is 'the Nicest Dude in Rock", or this Tumblr titled "Reasons Dave Grohl is Awesome."
One great example of that comes from the 2006 mine disaster in Tasmania, Australia. After a small earthquake caused a collapse, two miners were trapped underground. Rescue workers were able to communicate with them after only a few days, but had to work carefully over the next week so that they could safely extract them. The rescue workers were able to build a small pipe to deliver food and supplies to the trapped miners, and to keep their spirits up they sent down iPods for them to listen to. One of the two miners requested Foo Fighters songs for his iPod, and when Dave Grohl heard of it he sent along a letter to the miners. The letter read, in part: "Though I'm halfway around the world right now, my heart is with you both, and I want you to know that when you come home, there's two tickets to any Foos show, anywhere, and two cold beers waiting for you." The miners were safely rescued in May, 2006, and in October of that year Grohl kept his word, treating one of the miners to a show and meeting him for beers afterward. In fact , Grohl went one step further: he wrote a song called "Ballad of the Beaconsfield Miners" that he debuted at the show and later included on the Foo Fighters' album Echoes, Silence, Patience, and Grace. Pretty cool stuff.