Deacon: the most easily pleased Fallout 4 companion
Fallout 4 has a ton of perks. Perks can be unlocked after leveling up, found in skill magazines, and even earned through becoming friends or lovers of your companions.
Once the player character reaches maximum affinity with any companion, they are granted a unique perk that cannot be acquired anywhere else in the game. These companion perks are often extremely powerful and well worth the time required to earn them.
So, how do you reach maximum affinity with companions? Do the things they like! Most companions have a code of ethics that they'd like you to follow. MacCready, for example, will do just about anything if there's good money involved. On top of day-to-day activities, certain game changing actions will largely affect some characters' affinity. These usually come into play when completing faction quests.
If you've been wanting to start collecting companion perks in Fallout 4 but aren't sure where to start, you'll want to join the Railroad. The companion associated with the faction, Deacon, might be the most easily pleased companion in the entire game. This likely stems from his shady nature - we don't know exactly who or what he is, and why he does things.
Here's the twist: do we actually care when he is basically giving away free stealth damage? Deacon's perk "Cloak & Dagger" offers players a permanent +20% sneak attack damage and +40% increase on the effect duration of Stealth Boys. Coupled with other stealth perks, this bonus can result in a total of 5.3x bonus sneak attack damage.
How to Make Deacon Happy
So how do we please this master of disguise? Simple, do just about anything! Whereas most companions have one set day-to-day activity that grants you affinity with them, Deacon likes it when you hack computer terminals, pick locks, and be nice to people who deserve it. He doesn't care if you're sarcastic or if you try to weed out a little extra money - unless Synths are involved (in which case he'll dislike it).
On top of all of this, Deacon will love it if you complete Railroad missions. Even minor Railroad events like talking to Tinker Tom for the first time and taking his side will grow Deacon's affection.
Unfortunately, Deacon cannot be romanced, meaning that it will take a little extra time to complete his affinity boost. This, on top of the fact that you can't be a killing machine, destroying everything and everyone in your path with him alongside you, is the only downside to employing Deacon.
Where to Find Deacon
Deacon is a spy for the Railroad, an underground Synth sympathizing organization. In order to have him join you as a companion, you'll need to find the Railroad and undertake an initiation mission.
------------ WARNING! MASSIVE SPOILERS AHEAD! ------------
If you want to find the Railroad on your own, avert thine eyes! You likely won't hear of the Railroad until you get to Diamond City. Here you'll be able to find a couple holotapes detailing joining the Railroad. The only one I remember the location of is on a dresser in the top floor of Fallon's Basement. Once you grab the holotape and listen to it, you'll be given the Road to Freedom quest.
To start the walk along the Freedom Trail you'll have to enter Boston Common. From here you'll be given a red line painted on the ground to follow through the city to a bunch of local landmarks. If you plan on investigating these landmarks as you go, please bring a Fat Man with at least 3 mini nukes to the Massachusetts State House. I'll let you figure out why all by yourself.
As you travel through the city and visit these landmarks you'll notice red markings on seals embedded in the ground (they sort of look like manhole covers), spelling out a code. Since we're already in the spoiler section, I'll just go ahead and tell you that the code is R-A-I-L-R-O-A-D. I bet you never saw that one coming.
At the end of the Freedom Trail, you'll arrive at the Old North Church. Head through the basement to the catacombs below, enter the code when you come to the final wall and you gain access to the Railroad's secret base. Here you'll converse with Deacon and Desdemona - the leader of the Railroad - for the first time and receive your initiation quest.
There you have it! Deacon, his perk, how to please him, and where to find him! He is incredibly easy to raise affinity with and his perk provides one of the most massive boosts in the game. For these reasons I recommend you befriend him fast!