A lot of perfecly ordinary people routinely have their DNA frozen. They can be used for in-vitro fertilization, and there's no fundamental reason in the future why they shouldn't be able to clone an exact copy of a DNA donor.

Of course, a human being is the sum of his experiences and memories, not of his component physical parts, even if we reconstruct an exact duplicate all the way to the sub-atomic particle level. Your clone would be like your identical twin, perhaps identical in appearance and physiology, but a separate distinct personality, another person entirely. They might share a few personality traits with you, but they would not be you, they would have a different history and a different consciousness.

People who seek immortality through cloning don't fully understand this. I might like to live forever, but I really don't care what happens to my clone after I'm dead. He ain't me.

Robert Silverberg once wrote a novel about how a person's consciousness (or "persona") could be copied and uploaded into a computer memory, and later downloaded onto another brain, and the persona could share that brain and body with another person. (It was impossible to download into a corpse). The downloaded persona would be able to communicate with the host brain, and experience everything he experienced, but would have no access to the host's motor functions, so the persona could not "take over". Of course, a strong persona could psychologically dominate a weak host personality and gain control that way, or even drive the host into madness.

It gave the downloaded persona a chance to live again, although vicariously in another body. The recipient could use the persona as a friend, counselor, or adviser, (although they sometimes wound up hating each other, with comic or tragic results) but the persona would only have access to memories of his own life up to the moment of the recording. If he died, the resurrected persona would have no memory of anything between the last recording and the moment of death.

Most people who subscribed to this service had recordings made about every six months, updating new experiences into his record. The idea was that when you were finally downloaded into someone's head, you would have memories of your whole life except at most the last six months of it. Previous copies of your persona were supposed to be destroyed, by law, but of course, particularly talented people (like business tycoons and financial geniuses) had personas in high demand, and there were bootleg multiple copies on a flourishing black market.

Silverberg, as usual, has a lot of fun with this concept, but there is a deep philosophical point behind it all. If the human personality and consciousness is indeed just software and data that can be copied onto different platforms, then just what does the concept of conssciouness really mean? What is the soul? What happens if a persona meets itself? What happens if you time travel and meet yourself in the past or future? What about the Star Trek transporter accident that creates multiple copies of the same person?

As for the idea of multiple personas in one physical brain, that may not be out of the question altogether. It may be the origin of schizophrenia, multiple personalities, or even the left-right brain duality. The psychologist Julian Jaynes argues very persuasively, using ancient texts and modern medical literature, that human beings used to be like that all the time. Read his "The Origins of Consciousness in the Breakdown of the Bicameral Mind." There's plenty of room inside us for others. We are all a multitude.

Grace Slick wrote a song about it...
from "Schizoforest Love Suite", vocals double-tracked, of course.