I agree here. As we say many times on this board, you are in control of your career and your path. There are always going to be difficult people. When I was hired, I had a CAD/prototyping guy that was a major pain in the ass thinking I was coming in to take his job. He had been here for 20 years and was set in his ways. I had no desire to do what he did, nor did I ever try too, but when he saw me do rough mock-ups as part of the design process, he thought that was his turf and I was stepping on it. I just continued on with my work, built up design and design process. He is now gone with a sour reputation, I now manage ID and design is thriving. Did it suck in the process, yes, but management saw where the value was and EVENTUALLY did something about it.
The bottom line is you have to remember that this is a business and right or wrong, designs need to go out the door. If a firm or corporation is used to doing something a certain way they will continue to do that until they are shown better results. In your co-workers case, he/she has shown a way of working that has delivered results. They may not be the best results, but they are results. You now have the opportunity to show better results than what has been done in the past. He/She obviously sees your talent, understands your capabilities and is threatened by this. You need to ignore that and only focus on showing quality results that changes the current bar. By doing this you will have more important people on your side like upper management. Remember, you were hired for a reason. Someone obviously sees a need for a change.
hope this helps,
J