H.P.Lovecraft was a writer of horror/science fiction stories who did most of his work in the 1920s/1930s. Since his death in 1937, the appeal of is fiction has grown and grown. Many contemporary horror writers, artists and filmsmkers cite him as a huge influence and people continue to read, re-create and re-work his ideas as Ramsey Campbell noted:
“Howard Phillips Lovecraft brought the 20th Century horror story up to date, out of Victorian occultism into the realm of contemporary science without losing its sense of mystery”
To anyone new (or new-ish) to the work of H.P.Lovecraft, could start with this great 2 minute video that introduces his work and ideas:
The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the deadly light into the peace and safety of a new dark age.— The Call of Cthulhu by H. P. Lovecraft
And with this quote begins the short story The Call of Cthulhu by HP Lovecraft, a work that like no other, defines the Cthulhu Mythos. HP Lovecraft was a writer in the 1920′s and 30′s whose short stories and novellas helped define the modern supernatural horror genre. Never particularly popular during his lifetime (he would die young a pauper) he has been highly influential to many important modern day writers (most notably Stephen King). HP Lovecraft’s works are growing increasingly popular. Once only enjoyed by nerds and horror fans, his works are attaining mainstream popularity. James Cameron and Guillermo del Torro even wanted to make a film of his longest work At the Mountains of Madness.
As for the role playing game (RPG) Call of Cthulhu – Chaosium have a good section that introduces the game. There are also free eBooks for his work here, audio versions here and here, along with web versions.