It is based off a character I created. He is a hermit who lives in the mountains and writes books about magical creatures and immortals. He wrote a book called "1001 Ways to Kill an Immortal" but wrote it under the pen name "Nick B Rowler" so that the immortals could not track him down. So for a time, Nick B Rowler was sort of used as a stand in for "John Doe". For a time I had "I'm not Nick B Rowler" written on my DeviantArt account, more or less referring to someone who does not exist.
The name was also useful for usernames, replacing "Lilnanny" which tended to be snatched up. I decided to use it for my Tumblr account but dropping the B to avoid being called Nick Browler. But the name has been floating around longer than that, it appears in a fanfic I wrote back in 2007.