Here's a list of EDH Generals that are made to help change and alter the decisions people make.
Before anyone asks, all of these are made for Multiplayer games, since Singleplayer EDH is entirely aggressive.
Karn, Silver Golem - The main thing to look at is his activated ability. If someone is going to take a lot and only has artifacts, you can help them out. Sure, they have to sacrifice them usually, but it's worth it to make a friend. Not only that, but if it's a troublesome artifact, it can be a win-win for you sometimes (they'd thank you for the save, you'd have one less artifact to deal with).
Alternatively, if you have an enemy and someone's boardwiping, turning their artifacts into creatures to teach them a lesson.
Phelddagrif - The epitome of EDH politics, Phelddagrif is the only general to have a deck strategy made because he exists: Group Hug. His entire repertoire of abilities are made to give your opponents and advantage and simply, to make friends.
Someone being attacked? Give them a hippo or two! Someone on their last bits of life? Give them a boost!
You rarely win with his deck, so prepare to always come in second. You might be able to get away with a mostly blue draw deck and hope for a mill victory, but other than that, don't try any voltron/exalted stuff.
Heartless Hidetsugu - His main idea is to make pain universal. Instead of making friends through helping them, you help kill people. His ability doesn't target anyone, so it both helps and hurts everyone.
Lastly, if you have a Furnace of Rath or Gratuitous Violence out, you kill everyone with even life in one sweep. In that note, make sure you have odd life when you do that.
Patron of the Orochi - This is essentially a Seeborn Muse on crack that will always benefit you, but can benefit other Green players (is amazing with Seedborn Muse out as it is). Since it grants a huge bonus, Green players will not want you to die. Non-green players will definitely get angry, but the love from green players may over-weigh that. Use when you know you'll be playing with a Green player.
Shizuko, Caller of Autumn - Basically, she's a Magus of the Vineyard with a little bit more help for your opponents. Since you're not the first to benefit from the effect, you'll always never be on top with the mana boost. However, like Patron, you and green players will benefit the most, but unlike Patron, everyone gets something. Almost never receives hatred, and is never the target of singular spells.
Michiko Konda, Truth Seeker - The closest thing to a No Mercy general. Although it doesn't help anyone, NO ONE with want to attack you when there's others to attack. Even when there's just one person left, they'd rather not attack unless they know for sure that they're going to win then and there.
Mangara of Corondor - Mangara is a very trap-like general. If something attacks you, the trap activates and closes on whatever is going to hurt you. Isn't helpful for others, but makes you less of a target and can help save/ruin people.
Ith, High Arcanist - Well, they had to make Ith do exactly what his famous maze does. Helps people and stops others from swinging with their biggest threat. His cost is a little high, considering Maze is technically free.
Saffi Eriksdotter - S