Pfizer is an American pharmaceutical company that produces a number of popular prescription medications including Lipitor, Zithromax, Viagra and Celebrex. The company had its origins in Brooklyn in 1849, when two cousins, Charles Pfizer and Charles Erhart, started a fine chemicals business. The business was successful, and by 1906 its sales had reached $3 million. After Pfizer chemists became experts in the fermentation process that creates citric acid, they put their knowledge to work in making penicillin during WWII. Pfizer's stock went public on April 8, 2004, and on January 26, 2009, the company pledged its intention to purchase competitor Wyeth.