Anakin Skywalker, the never-ending plethora of layers to peel. And the people he surrounds himself are prime real estate to peel through, namely Padme, Obi-Wan, Sheev and R2-D2 (not quite five but definitely the most impactful).
The clearest impact is Padme, because she is the one who eventually will bring out his inner darkness. The question, though, is not what she causes him to do, but who she causes him to become, a liar and someone who believes he can do whatever he wants. We see throughout The Clone Wars he is evolving into a perpetual liar (or maybe it is just a certain point of view). For instance, he goes off to save R2 despite being ordered not to; time and again serves his own ego by following unconventional methods to get the job done. Now, the truth is it usually works out well for him, but it will be a domino in his downfall. Anakin’s determination to do things his own way motivates him into believing he can single-handedly (using Palpatine’s knowledge and eventually overthrowing him) save Padme from her imminent death. We all know where that leads.
As it regards Obi-Wan, one would think they they are nothing but polar opposites. The calm, cool, and collected Obi-Wan. The brash, overconfident, head first Anakin. While this is true, they have a great influence on each other, and Obi-Wan rubs off on Anakin a good bit. Obi-Wan has, in a sense, traveled the path Anakin is traveling. In The Phantom Menace, he is the headstrong one who has to be reigned in by Qui-Gon. Later, Anakin is the headstrong one having to be reigned in by Obi-Wan. While we don’t know who might have influenced Obi-Wan into his headstrongness, Obi-Wan still has a bit of that in him that influences Anakin. For example, at the end of Attack of the Clones, Obi-Wan is ready to rush in and fight one of the greatest swordsmen of all time, Dooku. True, he plans on having Anakin help him, but you can still see that glimmer of wanting to get the job done and the “go get it” mentality we saw with Maul in the previous film.
Obi-Wan is also fiercely loyal, which is a big attribute that rubs off on Anakin, who is always willing to fight for his friends and family (re: Ahsoka, Padme, Luke, etc). The same could be said for R2-D2. We numerous instances in The Clone Wars where Obi-Wan and R2 prove their loyalty. Satine. C3P0. The Jedi Order. D-Squad. Troops. Padme. Anakin. Anakin.
The biggest mover and shaker of Anakin’s life, however, is Sheev Palpatine. As Saw Gerrera would say, “Lies! Deception!” The lies and deception of Palpatine lead Anakin into becoming Darth Vader, which really messes up the whole “average of the five people you are around” thing. Or does it? The bits of Obi-Wan, Padme, and R2 seem to remain in the Sith that he becomes; the secrecy (which he also learns from Palpatine and the Sith way) and the loyalty (to the Empire and eventually Luke) fade but never fade fully away. Still, Palps does cause Anakin to question the Jedi and all that they represent, as he does, and to consider that there are other paths to getting the job done, as Palpatine has also done.
Anakin is the epitome of being changed by the people you are around and the environments you are in. The bright, bubbling, optimistic slave boy, influenced by his childhood companions and the always positive Shmi, becomes a downtrodden, dark side wielding pool of failure known as Darth Vader because he ran in the wrong circles.