WWE have an article on their official website featuring Rener Gracie (of the Gracie family who are considered MMA royalty), discussing the Kimura Lock that has been used by Brock Lesnar on WWE television in recent months.
Gracie stated that the hold goes as far back as early Japanese jiu-jitsu and Judo and people even trace the origins of Japanese jiu-jitsu back further to India thousands of years ago, meaning that the hold has been around forever, however it’s only recently becoming very popular because of its successful use by professional fighters. Gracie went on to note that the Kimura is a shoulder lock, originally called the Reverse Ude Garami in Japan, which means the reverse arm entanglement, an inverted version of the key lock.
Gracie then talked about the recent Frank Mir vs. Antonio “Minotauro” Nogueira fight in which Mir broke Nogueira’s arm with the Kimura stating, “It goes to show how serious the move is. Even though you might feel the pain and you might not want to tap, you have to. Because if you don’t, you’re going to pay for it. We always say at the Gracie Academy, recovery time from that lock is six days if you tap, six months if you don’t.”
More is available at this link.