 Later, his mother Julianna appears in the episode " Inheritance " and reunites with Data, though the crew discovers she was an android duplicate built by Soongafter the real Julianna's death, programmed to die after a long life, and to believe she is the true Julianna unaware of the fact she is an android. Faced with the decision, Data chooses not to disclose this to her and allows her to continue on with her normal life.
<meaning-changed>  Later, his mother Julianna appears in the episode " Inheritance " and reunites with Data, though the crew discovers she was an android duplicate built by Soongafter the real Julianna's death, programmed to die after a long life, and to believe she is the true Julianna unaware of the fact she is an android. Faced with the decision, Data chooses not to disclose this to her and allows her to continue on with her normal life.
 Later, his mother Julianna appears in the episode " Inheritance " and "I, Mudd"), Data was often referred to as being unique in the galaxy as being the only sentient android known to exist in the episode "The Most Toys" (save the other androids created by Soong).See the Star Trek: The Next Generation novel Immortal Coil, which explains what happened to all of these in the timeframe between the original series Star Trek and The Next Generation and how they relate to Data and Dr. Soong's other androids.