There are people who put "I am very serious because I do very important job" mask every morning before they come to the office. Don't do that! Smile! Those who really have to judge you will do that based on results of your work, not your posture. I try to smile as much as I can because I like to show everybody that I can do my job with ease.
You're right, knowledge alone will not make you famous. Pretending that you're famous and important will neither. What you really want to be famous of are the results of your work, your relationship with colleagues and your positive influence to them.
