In the spy world, a 'legend' is a false biography. Not a cover story, which is often temporary and mission-specific, but an entire history, all the blanks filled in.
A good example is LeCarre's SMILEY'S PEOPLE. One of the characters tells Smiley, "Karla is looking for a legend for a girl," and this is in fact the engine of the story. The old Russian emigre lady whose daughter she believes lost to her is persuaded to apply for her daughter's release, or expulsion, from the Soviet Union on what she's told are humanitarian grounds. Why she thinks such a thing would be granted without strings attached is another question, and she's nowhere near as naive as her clumsy handlers imagine. The point, of course, is that the one girl's background story can be substituted for another's, as a convenient fiction, and how this plays out, and why, is the plot of the novel, which I won't try to unravel here.
Edward Jay Epstein, some years ago, actually wrote a book titled LEGEND, which suggests that Lee Harvey Oswald's years in Russia were a carefully constructed KGB fabrication. You can buy into this or not, but it's a fascinating premise. Norman Mailer and Lawrence Schiller later plowed this same ground, with better resources, and came to the exhausted and disappointing conclusion that Lee was no more than an unhappy loser, without any depths to plumb, and the Russian security services had written him off as an embarrassment. There are always going to be unanswered questions about Oswald, but it's probably safe to say he was never a target for KGB recruitment.
A far more sinister spin on this is Richard Condon's THE MANCHURIAN CANDIDATE, which was published, if you can believe it, in 1959! (The movie was released in '62.) The story itself is about brainwashing and the Red Scare---an oxymoron, perhaps?---but for our purposes, the significance isn't political. Raymond, the sleeper assassin, has been programmed, as is everybody in his platoon from Korea. He's been supplied, in effect, with a legend. In this case, a set of implanted memories, but the end result is the same. A false narrative, an assembled history, becomes received wisdom, and accepted as authentic.
It's just as plausible to erase our own past, or sanitize it. Think of all those happy darkies, beating out barefoot rhythms, in the plantation South. Or our comfortable ignorance of the Japanese internments during WWII. Or simply the fiction that we've outpaced or outgrown ethnic hatreds and religious intolerance. What makes this century any different from, say, the 14th? The eradication of disease, perhaps, and the Black Death no longer the hand of God, punishment for our sins. Then again, contemporary weapons of war are that much more effective than the mace and the longbow. For sheer barbarism, can the Middle Ages– the massacre of St. Bartholomew, the Mongol horde, the pope giving his blessing to holy war---bear comparison with the past hundred years, in economies of scale? It seems more than a difference of degree. But for this, too, our collective memory supplies a less complicated substitute, a sense of moral superiority, of avoidance, or denial.
What if it were possible to reinvent yourself, to escape your personal history, to slough it off like a chrysalis, to create an entirely new identity, to become a different character, cast in an altogether different drama? A sort of Witness Protection Program, where you hide in plain sight. What imaginary model would you choose, what secret self? The problem being that the world around you wouldn't change. You might be thinner, or bolder, or have better hair, but individual actions won't roll away the stone, or turn back the sea. Putting on the clothes of concealment isn't safety. Seen back to front, there is no new-found freedom. The legend is a trap, an illusion of choice. The fault lies in our stars.
If this seems too deterministic, or cynical, consider that reinvention, or camouflage, is a means to an end, not in and of itself the end purpose. Disguise serves as part of a larger deception, and to be effective, we don't simply act the character, we inhabit the part. We become what we pretend, and fade into the background noise. The danger is that when we shed our old skin, and grow a new one, older habits of mind have to be discarded as well. We are no longer who we were. Living a lie, we trust it to protect us. As the Russian proverb has it: "If you play the sheep, you'll meet a wolf nearby."