At every job I've had, I have attempted to be “the guy” when it comes to something. It's been as big as a major piece of technology (the ‘Citrix' or ‘Virtual computing' guy) and as small as a piece of software (the ‘Excel' guy).
It's important to be ‘the guy' or ‘the girl' at something for one reason: People will think of you.
In business, you can be better at something than anybody else on the planet, but if people don't think of you first, then it's pretty much all for nothing.
So, make sure they think of you.
The funny thing is that you don't even have to be expert level at what you do. Just so long as you can answer the questions that are presented to you within a reasonable amount of time, you're good.
When I was the ‘Excel guy' at a recent job, I got the reputation pretty early on. I happened to help someone with a problem who used it a lot and who did a lot of talking in the department. Word spread quickly and people asked me Excel questions all the time.
My dirty little secret was that, for many of the questions, I didn't know the answer off the top of my head, and simply used Microsoft Help or Google to figure out the answer. I'd look it up, try it out myself to make sure it worked, then head over and show off my mad skill as ‘the Excel guy'.
It worked because it kept me talking to people that I might not otherwise talk to. That can never hurt in business where it's all about networking. I'm pretty sure I even got asked an Excel question or two by people with Manager or Director (or better) in their title, and that was double bonus day.
So, find something that you can be ‘the guy' or ‘the girl' at and get cracking. Don't make a big deal of it, but if you can quietly take on that role, it can only help your reputation.