The perfect family
Doctor's Family Program Beta-Rho was a holoprogram written by The Doctor to create a holographic family for himself, in an attempt to understand what it was like to have one.
In the original program, The Doctor had a wife, Charlene, and two children, Jeffrey and Belle. The Doctor's family was an unrealistically agreeable, "ideal" family. Lieutenant B'Elanna Torres edited the simulation, giving it a greater degree of randomness and also adding realistic character flaws and disagreements between the family members. Torres' version also allowed for an unexpected tragedy, which caused The Doctor a great deal of confusion and pain. Initially he ended the program without seeing his daughter's death through, but he later changed his mind, and stayed with her until she died. (VOY: "Real Life")