For the purposes of this article, I will refer to him as M. Bison (Vega in the Japanese version).
If we follow the deadly "rivalry" between Ryu and M. Bison in the Street Fighter universe, we come across three main messages that the Street Fighter team are trying to tell us about human nature.
Friendship Conquers All
Perhaps the blandest of the three messages is that friendship conquers all. This comes through most notably in the Street Fighter Alpha 3 endings, where Ryu is evidently saved from the “Hado of Murderous Intent” because he recalls the friendships he has made in the past.
The “friendship” motif can be witnessed through other endings, though. In his ending, as Ken practices Shoryukens, he says, “Wait for me, Ryu.... I'm not the fighter I used to be.... With my own way, I'll test my skill and...improve myself!” Sagat is deeply disturbed by M. Bison's manipulating Ryu, and after the fight, he makes sure that Ryu will be okay for their next fight. Sakura uses herself as a human shield so M. Bison cannot harm Ryu, and after she is hit, Ryu regains the strength to defeat M. Bison. Multiple endings point to the idea that every street fighter overcomes the embodiment of pure evil because they were able to draw upon the power of friendship.
Notably, M. Bison appears to have no friends, or if he does, they act more as business partners. The only true admirers and friends he seems to have are Cammy, Juni, and Juli - three clones made from his own DNA. As if this weren't narcissistic enough, Bison also decides to terminate the three, because they are either gaining too much free will, or are no longer useful to him. It is M. Bison's narcissism and opportunistic nature that causes his downfall. While he has the raw power of evil on his side, he will never be a match for Ryu or any of his friends because he lacks the one thing that defines us and gives us all strength in our hours of need - friendship.
“The Fight Is Everything.”
The message is less apparent in Street Fighter II, but it comes out fairly blatantly in Street Fighter Alpha 3. Ryu, Ken, Sagat, Sakura, E. Honda, Eagle... many Street Fighters from the early days pursue nothing more than the fight.
The message is surprisingly universal. Back in Homer's Odyssey, we see Odysseus traveling from place to place, desperately trying to get home, only to murder everyone upon his return (in a rather deus ex type fashion). In Philip K. Dick's Do Androids Dream of Electric Sheep? Rick Deckard spends the majority of the book trying to discover his identity and purpose. The book is centered around the journey, and only a few pages are dedicated to his killing the remaining androids. Even in Mihaly Csikszentmihalyi's Flow: The Psychology of Optimal Experience, Csikszentmihalyi proposes that it is not the ends to which we should look for satisfaction, but the journey that takes us there. That, he says, is how we obtain happiness.
Another interpretation is that learning is more important than failing. After each defeat, the fighters graciously congratulate the opponents (for the most part), and recount the lessons that they have learned (usually that they need to get stronger). The message is very close to John Stuart Mill's philosophical ideas that people need to think for themselves. Mill was largely against government intervention because people wouldn't learn anything from an authoritative power dictating their lives. Rather, they would simply be lemmings, stuck to follow the rules others have set for them and never growing to their true potential. Juni and Juli only evolve when they learn to think for themselves and appreciate the art of training and fighting.
As Juni and Juli learn, it's not fulfilling the directives that matters most to shaping our personalities. It's what we have learned along the way.
The Definition of Pure Evil
The most important and least obvious theme in the Street Fighter universe is the perversion of the human spirit. To gain a better understanding of this, we need to go back to Street Fighter II.
Street Fighter II's storyline centered around a fighting tournament. In Ryu's ending, M. Bison graciously accepts second place, as Ryu walks off in the distance. M. Bison isn't seen as a totally evil character in the game (though, notably, he has killed Chun Li's father and caused Guile a lot of grief). He's simply the person in charge of the tournament.
That M. Bison is in charge of the tournament speaks to his narcissism. The player can assume that he has organized the tournament as a way of showing off his martial art skills. That narcissism ends up being his downfall in Street Fighter Alpha 3, but it also shows another universal theme - the corruption of greed.
Vegeta from the Dragonball Z universe is an interesting parallel. Driven by his need to defeat Goku, he does anything to become stronger, including becoming a slave to Babidi. In a similar fashion, M. Bison is driven by his need for power, and thus taps into Psycho powers in order to defeat Ryu. He's no longer interested in testing his skill or showing off. He simply wishes to defeat Ryu, and thus weaves a path of destruction along the way.
An interesting question to ask is, “Why didn't Sagat follow the same route?” Surely, Sagat wanted revenge on Ryu as well, but by the end of Street Fighter Alpha 3, he has notably toned down and considered Ryu more as a rival as opposed to an enemy. The answer lies in the scar on his chest.
The scar on his chest symbolizes a permanent imprint Ryu has made on his life. We notice that Sagat is less narcissistic than Bison because, though he has the scar on his chest, he wears it proudly. He takes no medications to remove the scar, nor does he decide to wear a shirt to mask it. Sagat, subconsciously, realizes that he needs to appreciate the path of life, and so always shows the scar that has changed his life the most.
The definition of pure evil, then, is absolute selfishness and friendlessness.
Conclusion
The combination of lust for power and narcissism explains both why M. Bison becomes the “ultimate evil” in the Street Fighter universe, and why he can never defeat Ryu in a fight. As human beings, we should always remember that we are greater than the sum of our parts, and that the path to success might well be more important than the success itself.