Durance - +1 Con/+5% Max Health
Zahua - +1 Con/+5% Bonus to Beneficial Effects (Edited per Patch notes)
Grieving Mother - +1 Res/+5 All Def against Int Afflictions Attacks
Devil of Caroc - +1 Dex/+1 Armor Pen against Kith (edited per Oriz)
Eder - +1 Mig/+2 Deflection
Mahena - +1 Mig/+5 All Def against Mig Afflictions Attacks
Kana - +1 Int/+5 All Def against Dex Affliction Attacks
Aloth - +1 Int/+5 Reflex
Hiravias - +1 Dex/+1 Slash Armor
Pallegina - +1 Res/+1 Shock Armor
Sagani - +1 Per/+2 Accuracy (while attacking same target as an ally)
Gift of the Machine - +1 Mig/+5% Max Health
Most of this was taken from reddit and other post. Just decided to compile it into a neat thread.
If you are building a custom PoE1 background (as I did myself) you may only care about characters who actually appear in PoE2. So careful when choosing. Aloth, Eder, Pallegina are characters who you can recruit as companions in PoE2, which enrich the storyline somewhat. The rest in my opinion are expendable, again it goes my RP ideals, but one can say that during the Watcher's death the part restored from his soul was changed somewhat, and so decisions made during PoE1 era, are in a sense against your current views. Assuming you are Benevolent character (Lawful Good, Neutral Good or Chaotic Good).