Seven's idealized version of herself
Seven of Nine Alpha 3 was one of a series of holoprograms created by Seven of Nine in 2378 to help her improve her social life.
In the program, her Borg implants had been removed and she began a relationship with Chakotay. This led to a form of holo-addiction, and engaged the fail-safe inhibitor in her cortical node, which could have killed her. Seven eventually decided to discontinue her use of the programs, as it was an inefficient use of her time. (VOY: "Human Error")