Zombies. Fact Or Fiction?

Ok, I’m not talking about the dead rising from the grave and killing all of humanity, but people that don’t die. there is one jellyfish that is biologically immortal, wich is kinda neat but a bit off topic.

I’m talking about some sort of military experiment, you have to admit, by now they must have tried to make a soldier that does not die, possibly messing up the process somewhere through, rendering brainless or mad. What do you think? Do you think that somewhere they are hiding an experiment like this?

Also, do you think we could ever make a human that is biologically immortal, in the way that that jellyfish is?