I would say either boxing, karate, or wrestling. I'll explain each individually.
Boxing: You gotta start somewhere in the striking department. I would suggest if you just want to learn the basics, just learn the block, movements, jab, and cross. Muhammed Ali only had 4 punches in his arsenal with no shots to the body(major wtf), but the way he put them together was so beautifully done.
Karate: If you want to learn the basic kick or two, as well as good self defense and average striking, karate is the way to go. That was my first style learned, but I used that as a stepping stone to progress into other striking arts like Muay Thai and Western Boxing.
Wrestling: Whether it be submission, amateur, Greco-Roman, whatever, it will all help you. Any brute thinks he can effectively "wrestle", but that is just them applying a headlock. Everyone wrestles, whether they are interested in MMA or not, but only a very slight percentage of those know how to wrestle properly.
If you want to go more advanced try Muay Thai or Brazilian Jujitsu.
Jack Johnson: Boxing's greatest Heavyweight champion.