There has been three people who have operated as Chemistro in the Marvel Universe. The first Chemistro was Curtis Carr, the creator of an "alchemy gun", capable of changing one chemical substance to another (for example, lead into gold). When Curtis's company fired him over the legal rights to the gun, Curtis fought back as Chemistro and used the gun as a weapon to destroy the company. During a battle with Luke Cage, Curtis changed his own for to steel, which promptly crumbled away. Humbled, Curtis willingly went to jail, served his time and is again a productive member of society.
The second man who operated as Chemistro is not worth mentioning beyond this sentence.
The current Chemistro (and one pictured here in custom Minimate form) is Calvin Carr, Curtis's younger brother. He stole the Chemistro identity and alchemy gun from Calvin, and while he hasn't shot off his own foot, Calvin has yet to do anything of note with his power. Lacking the imagination to gain power or riches (hint: lead into gold), Chemistro is currently rolling with the Hood's gang of super-villains.