For the sake of helping to turning around an entire ball-club and becoming the face of success in the majors has to be...
Jeff Bagwell for HOF'er!
Not only did he help dig the Astros out of bottom-scraper status in a major way, he elevated the Astos in such a way as to, in the mid 90's, find division success again and again and again! My perception may be a bit-skewed since the mid 90's were the time when I moved beyond baseball as fan of a simple sport to a fan filled with intrigue at the inner-workings of baseball in its entirety, but Bagwell was the face of the Astros at that time! Though the playoffs were unforgiving for the Astros - especially those darned first-round games - Bagwell gave Astros fans hope that they were on the cuff of something great. His play went beyond simple stats. His play built a story for Houston as a fan-base to become a part of. That's why we watch baseball anyway, isn't it!?
If you don't believe me, feel free to get into the inner-workings of his stats on wikipedia, ESPN or SI. I'm too lazy to cut-and-paste today!