Dungeon Siege III
44 Achievements
Maximum Charisma
You achieved the highest possible influence with one of your companions.
1.8%
How to unlock the Maximum Charisma achievement in Dungeon Siege III - Definitive Guide
However, playing around trying to do another achievement, I discovered a way to get infinite influence. Possibly even more than just one companion if you were so inclined. Only found out how to do this at the end of the game, so it is best to try it there - I will keep this spoiler free as well.
Only recommend this if you really want the achievement or ran out of options trying to gain maximum influence during your playthrough.
The Trick
Near the end of the game when you return to the first Legion Chapterhouse (points of no return and prior to entering the East Forest), there will be a room with spider webs all over, a save point, and two doors that open into the East Forest. When you open the first door using RB your companion will make a comment about it being an honor to fight by your side and shortly after the influence gain text will pop up.
After that, you can press the BACK button to see where you are influence wise with your current companion. Then turn around and save at the save point. Afterwards, load the same save file you just created. Then open the door again, even if the door appears to be opened still go up to it and there should be a prompt to open it. Your companion will speak again and another influence gain should pop up, check the progress meter to make sure it has advanced. Then just repeat the process of saving and opening the door, saving and opening the door - to earn the achievement.
If you have saved at the save point close to the last boss fight, you can back track all the way to the Legion Chapterhouse again. Go through the doors to the save point and then just reopen the last door you went through and it should prompt you again. Then save and repeat.
Felt it was necessary to also give credit to another player who figured this out before I did, from Elyoh's post on Xbox360Achievements.org - Frogcat from Playstation Network.
Below is a link to a dialogue guide, but I first want to provide a tip:
My recommendation is to increase influence with all your companions up to 75% before you get to that part. Reason for it is you will gain 2, 3, and 5 in a specific stat at 25%, 50%, and 75% influence with each character. You only get an achievement for 100% influence with one companion. 100% with everyone gives you nothing extra. Its worth going after these stat bonuses if you are playing on the hardest difficulty.
All influence is gained through quest related dialogue choices, and each companion requires a different answer to raise their influence.
https://www.primagames.com/games/dungeon-siege-3/primaguides...
Update 5/14/2017: the link to the prima guide above was open to the public when I posted it, but those jerks have locked it. Here is a link to a guide on Steam with a section containing + influence dialogue choices for each character: https://steamcommunity.com/sharedfiles/filedetails/?id=13867...
NOTE: the above link only has answers for the main game. The DLC offers more. Here are links each character's dialogue choices in Treasures of the Sun:
anjali: http://www.gamebanshee.com/dungeonsiegeiii/influence/an....php
katarina: http://www.gamebanshee.com/dungeonsiegeiii/influence/ka....php
lucas: http://www.gamebanshee.com/dungeonsiegeiii/influence/lu....php
reinhart: http://www.gamebanshee.com/dungeonsiegeiii/influence/re....php
Missable.
For this you should concentrate on one companion only and not change to the others. You should work on this on another playthrough if you want to get Circle of Friends as well. As soon as I got Circle of Friends, I stuck to one companion and was just short of reaching this. To view how far along you are, press and progress appears next to your companion as a yellow bar marked as 'Influence'.
This is also best attempted in offline mode as you could be working on one character and someone else could come into your game and start using a different character. Save regularly and reload at most of the conversations to try different options, this will allow you to see which ones will add influence and which won't.
If you have made all the correct conversation choices, this should appear by the time you reach the Spire.
See Circle of Friends for easy way to get this trophy.