Rambo - A surname chosen by a swedish immigrant to the United states.
Peter Gunnarsson chose the surname of Rambo from his place of origin, Hisingen, the northwestern section of Gothenburg, which is dominated by Ramberget mountain, meaning raven's or ram mountain depending on which dialect it was stated in.
He was actually an apple farmer, and introduced the 'rambo' apple into the colonial town of new sweden in 1637.
I believe it was the seeming duality of the original name that inspired the character name of the Rambo series movie.
However, the native people of the North American continent tie them together in legend.
"Bighorn Sheep (ram) were amongst the most admired animals of the Apsaalooka, or Crow, people, and what is today called the Bighorn Mountain Range was central to the Apsaalooka tribal lands. In the Bighorn Canyon National Recreation Area book, storyteller Old Coyote describes a legend related to the Bighorn Sheep. A man possessed by evil spirits attempts to kill his heir by pushing the young man over a cliff, but the victim is saved by getting caught in trees. Rescued by Bighorn sheep, the man takes the name of their leader, Big Metal. The other sheep grant him power, wisdom, sharp eyes, sure footedness, keen ears, great strength, and a strong heart. Big Metal returns to his people with the message that the Apsaalooka people will survive only so long as the river winding out of the mountains is known as the Bighorn River."
The Apsáalooke native americans are the source of that legend, their name was mistranslated by early interpreters as "people of [the] crows." It actually means "children of the large-beaked bird," a name given to them by their neighboring tribe, the Hidatsa. The Absaroka first encountered Europeans in 1743, two Frenchmen (the La Verendryes brothers from Canada), near the present-day town of Hardin, Montana. These explorers called the Apsáalooke beaux hommes, "handsome men." The Crow termed Europeans as baashchíile, "person with yellow eyes."
Between the Native American legend and the strangely similar legends surrounding rambo's (gunnarsons) home mountain of rambertget, it doesn't take much of an imagination to draw the inferences from both portrayed in the movie rambo character.
With that I would say 'Rambo' is not an acronym, but rather a history. Though I will admit it almost begs for an acronystic meaning.
Regards,
Gerald