Why does this one guy always win at Texas no limit?

I play online Texas no limit online and every time I play, there is this other opponent who always seems to win, I am really sick of this guy...no matter what I have he always wins even on some of my best hands and even playing tight...he`s not a maniac - but nobody seems to be able to beat him and he just stacks and stack and stacks.....how do I beat creeps like this? What is his secret cause I`m in the dark.