William Procter, a candlemaker, and James Gamble, a soapmaker, formed distinct companies. The two men, immigrants from England and Ireland respectively who had settled earlier in Cincinnati, might never have met, had they not married sisters, Olivia and Elizabeth Norris.
Since both their industries used similar resources, the Panic of 1837 caused intense competition between the two and as a result it led to discord with the family. Alexander Norris, their father-in law decided to call a meeting where he convinced his new sons-in-law to become business partners. On October 31, 1837, as a result of the suggestion, a new enterprise was born: Procter & Gamble.
This first P&G logo originated in 1851 as the symbol for their Star brand of candles. It was later altered to show the man in the moon overlooking 13 stars, which were meant to commemorate the original 13 colonies (British America).
For more info on this logo, see: http://en.wikipedia.org/wiki/Proctor_%26_Gamble#Logo_controversy