When I joined the company my co-worker was very nice; he taught me a lot of things, always paid attention to my questions and he really tried to help the most he could.
However, as time passed and I gained experience, I grew to the point of not needing his help at all. Now my contributions to the team seem to add more value than his and my boss constantly congratulates me in front of him whenever he comes to our offices. My coworker has been in the company for several years and is a valuable member, but he lacks initiative and he only does what he is asked to and no more. Since I have arrived, he spends most of the time unnoticed. It might also bother him that I'm 10 years younger and less experienced but we pretty much perform the same task and hold the same position (i.e same salary).
These facts have caused an extreme change in his behavior towards me: he doesn’t talk to me anymore, he barely shakes my hand when I say hi, and I suspect he is looking for any mistakes to make me look bad. I do not look for his praise or worship but I feel there was a change for the worse and really want to fix it. I just want to be in a stress free environment. I don’t really want to tell my boss or HR because, let’s face it, I am the new guy and there were no issues until I arrived. I really don’t have any interest in causing him any problems.
How do I proceed? If is not affecting the team performance, is it even worth to try fixing things?
Also, he's been here for a while and, as I stated before, he is still a valuable member. If our boss gets promoted, he will likely get his position and become my boss. If that happens and we haven't fixed things by then, I will be screwed. Of course, this is just a possible scenario. I don't know if it is even going to happen.
EDIT: So it has been a while since I posted this for the first time
I asked him what happened and he admitted he didn't like me anymore. He was not ok with the way I do things. I asked him to tell me specifically what was bothering him and that I was willing to change. He said there is not a particular reason.
I don't even joke around or make bad comments or treat him rudely. As a matter of fact, I get along with everyone but him. I think there is nothing I can do and I honestly tried to fix it but at this point I have stopped caring.