Shaun (synth)

S9-23, also known as Shaun, is a prototypical synth created by Father, and as such, lives within the Institute.

Background
Shaun was created by Father, or the real Shaun, using his own DNA as a base for the child's organic functions. Seeing the chance to use this Shaun replicant to further his personal agenda, Father instructed Kellogg to bring the child to Diamond City shortly before remotely releasing the Sole Survivor from their cryogenic captivity, giving them a trail to follow all the way back to the Institute.

By the time that the Sole Survivor arrives at the Institute to locate the real Shaun, they come face to face with the synthetic Shaun, believing him to be the real Shaun, in which the meeting is revealed shortly after to have been a test, in which the synthetic Shaun is shown to react negatively towards unknown variables such as the Sole Survivor.

It is mentioned throughout the Institute through overheard dialogue with random Institute scientists as well as Madison Li’s terminal that Shaun is incapable of aging and thus causes them great distress as he will remain a child for all of his life.

Other interactions
Should it be chosen to destroy the Institute, and so long as Shaun is rescued from the destruction at Father's pleas, the synthetic Shaun will periodically ask for the Sole Survivor to bring him specific items (i.e. a hot plate) so that he can 'take it apart', and in return, will build useful items, culminating in the creation of the Wazer Wifle.

Additionally, Shaun can be sent to a number of settlements, so long as their workbenches have been unlocked.

Should Shaun not be left behind in the Institute after its destruction, the synthetic Shaun will give the Sole Survivor a holodisk titled Shaun's holotape, as instructed by Father, saying "I didn't listen to it, so I dunno what it says, but I think it's important." The holotape, recorded by Father, reveals that he had programmed the synthetic Shaun to believe that he was the true son of the Sole Survivor, and pleads with them, saying "I would ask only that you give him a chance. A chance to be a part of whatever future awaits the Commonwealth."

Should the Sole Survivor leave Shaun in the Institute following its destruction, Shaun will remain behind, and become another casualty.

Appearances
Shaun appears only in Fallout 4.