A lot of people here (and mostly on Stack Overflow) don't have their real names as usernames. The same goes for github, twitter and so on. I put the links to those profiles into my CV so companies can see them, because that's my online identity. I've never heard of a company complaining about that. It's normal as long as you can prove that it's you.

For the real life and interactions with companies in person it's a different story.

While it's perfectly fine to want to stay anonymous online and use a nickname, if you want to deal with a real company, you will have to tell them your real name. 

If you have a work contract, that will have to have your actual name because of social security, tax and so on. In some countries you can pick an artist name that goes into your ID, but your legal name is still required for contracts.

Of course you might be able to explain to HR that you prefer to use your moniker and not your real name. 

I know someone working at a large, well-known company in Europe who doesn't have his name at his doorbell at home, and who never tells anyone his name. His coworkers in the office don't know it. His friends in that country don't know it. If he goes to hotels, he makes sure no-one oversees or overhears when he checks in, and none of his coworkers but HR know his name. Everyone calls him with the nickname he chose for himself, and that works for him.

As for the CV, you should use your real name. Unless you're an actor or performer probably. But then you wouldn't worry about a github account.

All the online accounts are just places where you show what you can do. If you use the same nickname everywhere, and that nickname is distinct, then it will be easy to find your work. That's good for you and for companies that are interested in you. But that's all they are. Screen names. Login data. You're still you, and for the real world, you need a real name.