ant man has been used by 3 ppl in marvel 616. lots of spoilers
hank pym is the best known ant man, among the top 9 smartest ppl in the world (include reed and stark) he invented pym particles to shrink his ass down to an ant, he created a stupid looking ant helmet to control ants, and thats it, other than being an original avenger. Currently the MCU has seemingly taken away hank pym's one and only useful claim to fame which is creating the super villian robot ultron. sometimes hank pym has retired being ant man and becomes giant man.
scott lang is ant man 2, he stole the ant man suit and saved his dying daughter, he's just an avg thief, so they make him an avenger, he's later on killed in avengers dissassembled cuz he sucks. his daughter then becomes stature (giant woman) and also dies too, cuz fuck that family tree.
eric o grady is called the irredeemable ant man, cuz he's shady irish prick agent of shield that found the ant man suit, he does some funny things but ultimately dies too, cuz fuck him his story was going no where.
the movie will probably have something like hank pym is a retired ant man, and scott lang broke into hank pyms old bat cave, stole the ant man suit, used it to save his daughter, got arrested, and hank pym got scott lang released to be ant man.