OMG Dates Back to 1917
Nowadays, the acronym OMG is so commonplace that it has been turned into a candy brand. The abbreviation, which stands for "oh my God," has been a mainstay since LOL and BRB and other well-known acronyms took over internet speech since typing complete sentences takes too much time. So you'd be excused if you assumed it was recent, occurring around the advent of the internet or texting, and only a few decades old.
Even though he might not have created it, the first person to say OMG is not believed to have been texting at the time. It appeared in a 1917 letter he sent to Winston Churchill. During World War One, he was an admiral who told Churchill, "I hear that a new order of Knighthood is on the tapis—O.M.G. (Oh! My God!) Shower the Admiralty with praise!
Lord Fisher has had a distinguished naval career and reportedly earned the highest grade ever on his tests. It may not come as a complete surprise that he invented this shorthand given his reputation for being a skilled communicator and his love of acronyms.