Kicking/Banning

What is the command to kick and Ban players? I tried the ones that I have seen and get player does not exist message. We had a player griefing in our server and couldnt get rid of him, shut the server down 3 times and he kept returning. Thanks in advance.

Thanks Galveston I figured out what I was doing wrong, I was putting the * around the name and it doesn't require it. I hate to kick people but when they come in and just start wrecking everything you have built and saying they will "report your server" just because you wont fight it's time to do something. I have met some really good people on here but there will always be that 10%. I don't really want to password it but it will definatly be the next step.

That will be my next option. Was just hoping that I could have mature people in my server, but maybe not LOL.