The Overseer (Vault 101)

The Overseer is the leader of Vault 101 and the father of your childhood friend, Amata. He and his wife rarely spoke to one another.

As Overseer, he is determined to keep the Vault closed to the outside world, at least for the general population of Vault 101. When James escapes, he thinks that the Vault 101 Dweller had something to do with it, so he sends his security after him/her. He orders the death of Jonas after James' escape and interrogates his own daughter during the the Vault 101 Dweller's escape. Depending on whether or not you kill him, Amata will react differently toward you.

If you do not kill him during your escape, he will tighten his grip on the citizens of Vault 101, which will result in a rebellion. Later in the game, if the player character travels near the Vault, their Pip-Boy 3000 will discover the Vault 101 Emergency channel where Amata was broadcasting a plea for help on a repeating loop, which reveals to you factional crisis in Vault 101.

When you converse with the Overseer, he reveals his fear of the Vault being contaminated with the outside world (due to his Vault's stated mission), and does not want to allow the youthful "rebels" from repeating the same mistakes the peers of his generation did when they left the Vault, only to never return. If you check his console, it is revealed that after you left, the Enclave contacted the Vault in an attempt to gain access, but the Overseer denied them entry as he would not trust the lives of the Vault inhabitants to outsiders.

He also regretted his actions during the night of you and your father's escape.

Note
If you kill Amata's father while escaping from Vault 101, Allen Mack is named the new Overseer, letting you do the Trouble On The Homefront Quest.

Appearances
Just like Vault 101, the Overseer appears only in Fallout 3.