The book “Language of the Civil War” by John D. Wright ($85 on Amazon.com!) published in 2001 says that the term originated with Confederate Vice President Alexander Stephens. His extreme intelligence overcame his small size (90 pounds) and unhealthy appearance. The term “Smart Aleck” is used to describe someone using sarcastic, mocking humor in an argument, and Stephens was said to have earned that nickname. Several other sources, including Wikipedia,  say the term “Smart Alec” was coined to describe a con man named Alec Hoag who ran a pickpocket operation in the 1840s with the help of two policemen. He is said to have earned the nickname when he wound up in prison by trying to cheat the two policemen out of their cut. I think the fact that the expression doesn’t appear in print until 1865 adds credibility to the first explanation even though the second explanation has more references.