For a while, what is now called the SG was the Les Paul. Just so happened that Mr. Les Paul himself didn't like the shape of the body and didn't want his name on that style of guitar. From Wikipedia:
"For various reasons (declining sales due to the high price, and strong competition from the popular, double cutaway design of the Fender Stratocaster), the Les Paul Model received a complete make-over in 1960. The model became thinner, and received two pointy cut-aways. This was done without Paul's knowledge, and when he saw the guitar, he asked Gibson to remove his name from the instrument. In 1963, the name of this model changed from "Les Paul Model" to "Gibson SG" (which stood simply for "Solid Guitar".)"