Rudrashtakam finds its origins in the Ramanyan written by the Great Goswami Tulsidas(16th century AD) in Varanasi, the Holy city of Lord Shiva. He was writing the Ramayan in the Vishwanath Jyotirlinga temple and it was due to the grace of Lord Shiva that it could be composed and thus dedicated this hymn in his praise.
Rudrashtakam in Sanskrit
It means:
All is One, One is All 