| Southern Comfort, or, as coined by your average drunk on-the-go, "SoCo", isn't necessarily a proper liqueur: it is closely related to bourbon, but has the basic properties of a mixed cocktail.
In the late nineteenth century there was a cocktail known as Cuffs and Buttons that was made by marinating peaches in bourbon and peach schnapps. The fruit and tang of the peaches made the taste of bourbon more acceptable to your average weekend drinker who wasn't exactly infatuated with the taste of straight whiskey. An enterprising bartender in Missouri changed the name of the drink to "Southern Comfort", and it became popular enough for a distiller to market that blend.
The resulting taste is a sort of carmelized whiskey that goes down almost too smoothly.
When using SoCo for making cocktails, one must be careful: like grenadine, it has the tendency to overpower the other ingredients. To quote Mel Brooks, "THE PEACH IS LIKE HITLER!". It is, however, a necessary ingredient for such classics as the Slow Comfortable Screw Up Against A Wall and the Alabama Slammer.
Personally, SoCo and Barq's root beer is one of the closest things to ambrosia on this earth. Honest. | 
