Scott Lang was the 2nd Ant-Man. He was created by David Micheline, and John Byrne.
Scott Lang used to work with electronics. He was unable to support his family and had to resort to stealing. He was caught, and put in jail, where his wife divorced him.
When his daughter Cassie, was diagnosed with a heart condition, he stole the Ant-Man costume from Hank Pym to steal enough money for an operation.
After he succeeded on stealing enough money and using for her daughter's operation, he was gonna return the suit to Pym when Pym let him be the new Ant-Man.