RoboCop

Short Answer: RoboVigilante

For most of the RoboCop franchise's run, the only people capable of turning a cop into a "robocop" would be a conglomerate with a name like OmniCorp (or LexCorp, or Oscorp...).

Today, though, such technology is readily at hand. Between the Internet, 3D printing, and other resources, it would not take $6 million to make a "Six Million Dollar Man"-esque cyborg.

In fact, look up the term "bio-hacking." People are already implanting chips into them hands and otherwise Borg-ifiing themselves. 

So what about this: A group of nerds tries going into a tough-guy bar, but are being bullied when our hero intervenes. He saves the nerds, at the near cost of his own life. 

The nerds run into the alley, pick him up but-- instead of taking his to a hospital-- they take him to their university lab.

His spine is broken and he'll never walk again, says one, a medical student. If we take him to a hospital, all they will give him is a wheelchair-- but we can do better.

At the lab, they pool their nerd skills, from medicine to robotics, to rebuild him. No, they don't ask his permission, but they figure, "Who wouldn't want to be upgraded like this?"

He wakes up and after raging at the nerds-- "What did you do to me?!?"-- he starts to learn to use, and even enjoy, his enhancements. 

They agree that the first place they need to clean up is their campus. There are bullies and drug dealers and so on. Our hero makes quick work of them and they flee.

But they soon return, with guns. Cyborg that he is, he is still mostly human and not bulletproof. The nerds procure a bullet-proof vest that he can wear under a light jacket. 

He also realizes that his abilities and bravery are not enough, and that he still needs to learn how to fight, and also control his super-strength so that he wins... but not by too much.

By now, the police are well aware of the situation and resolve to bring him in. They are waiting at the next brawl and as soon as he sees them, he freezes and cooperates. 

Brought in, the authorities agree to drop their charges if he joins them and undergoes actual police training. He says OK but he needs to bring his team with him-- if anything happens to him, they are the only ones who can fix him. The police agree. 

And a robo-vigilante becomes a robo-cop.

Either that, or an existing RoboCop gets hacked and controlled by someone evil and he had to use his human half to defeat his robot half.