Giving it a shot; I picked my favourite companions from New Vegas and FO4, respectively.
This companion is often sarcastic and cynical, but deep down they're just old and tired. Despite their often passive-aggressive comments they seem to genuinely like the player's company, often showing disappointment when left alone and eagerness when asked to travel.
This companion has a terrible habit of lying and is sometimes playful to a fault. They're fond of witticisms and verbal jabs, but behind their facade of aloofness, they're simply lonely and afraid to get close to anyone.
Both of them call the player "boss".
This is a bit wasted on me as I haven't played
Fallout 4 
. Could tell the first one was Raul though.
I'll try and describe characters from
Fallout New Vegas and
Fallout 3.
This character is a psychopath. While their actions may have good intentions, at least from their perspective, the character shows throughout that they care little for human life, and less remorse for stepping on other people's freedoms. The character is intelligent, educated and though they have pretensions of caring about humanity as a whole it is unclear how much the character really cares about others, and there is every chance that they are doing the things they do for their own benefit. The character dislikes ignorance in others, but it is unclear whether they actually care about educating people. They do not seem interested in what happens to those around them after they die, only in their own personal achievements. The character is calculating and violent, though they come across fairly civil in conversation, as long as their demands are catered to. They also have a fairly dark sense of humour, which, though infrequent, does come up from time to time.
This character is a psychopath. Their actions very rarely match the polite and calm demeanour they carry. While they act like they care about things and people their actions only put others in danger and ultimately harm society as a whole. Seemingly intelligent, as they have scientific knowledge, the character's intelligence does not fit their common sense, suggesting some kind of mental disorder like psychopathy.
@RoboStang To be fair, the main questline of
Fallout 4 is a straight up remake of
Fallout 3's.
