I'll start off by listing mine:
The T-800, Terminator 2: "I know now why you cry, but it's something that I can never do." Gets me every damn time.
ADA, Zone of the Enders: I think I'm the only one who played this game more than the MGS2 demo that came with it. I will never not laugh at the exchange of "You may speak like a human, but you're still a heartless computer, aren't you?" "That is correct. What is the problem?"
Codsworth, Fallout 4: He survives the nuclear holocaust despite not having a bunker and waits 200 years for you to come back. When you look at what changes his relationship with you, he mostly just wants you to be nice to people. I never swapped him out as my companion.
B.O.Y.D., Ducktales 2017: He's adorable. 'nuff said.
On that note, a deep cut - The Guardian from Thunder Force V (Sega Saturn/PS1). Apparently goes rogue and turns a army built around reverse-engineered xenotechnology (Actually the wreckage of the Rynex, the player's ship from the previous game) against humankind, turns out to have been parasitized by series big bad ORN. Just barely manages to retain enough control over herself to make the fight winnable through subtle yet deliberate strategic errors.
[Soldier/Human]
TF6 was a waste for many reasons, but the biggest problem was relegating the whole "The Guardian is repaired and bolted to the player's ship for a defensive last stand against the main ORN fleet" to a cutscene