In fiction, I mean. Had to shorten the title for the character limit.
My favorite is undoubtedly Porygon-Z from Pokémon. It and its two pre-evolutions (Porygon and Porygon-2) are sentient computer programs contained in floating, duck-shaped shells. What's interesting about Porygon-Z in particular, though, is the fact that it's implied to be infected with some kind of COMPUTER VIRUS. You use an item called a "dubious disk" to evolve Porygon-2 into it, and Z frequently goes through what look like painful, glitchy spasms.
It prompts some really frightening questions: Is this thing in constant pain? CAN IT FEEL pain? Are the program bugs tearing its psyche apart, if it even had one in the first place!? It's an entertainingly spooky take on intelligent AI gone wrong.
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They say perfection is the ultimate imperfection. Or maybe that's just what I say.