vs
QUICK ANSWER
"Ladrón" is a form of "ladrón", a noun which is often translated as "thief". "Atracador" is a noun which is often translated as "bank robber". Learn more about the difference between "ladrón" and "atracador" below.
el ladrón(
lah
-
drohn
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
b. robber 
El ladrón se escapó con un millón de dólares en efectivo.The robber got away with a million dollars in cash.
c. burglar  (from a building)
Un ladrón robó la tienda de joyería del centro comercial.A burglar robbed the jewelry store in the mall.
2. (electrical)
a. adapter 
Necesito un ladrón para conectar varios aparatos en la cocina.I need an adapter to connect several appliances in the kitchen.
el atracador, la atracadora(
ah
-
trah
-
kah
-
dohr
)This means that the noun can be masculine or feminine, depending on the gender of the noun it refers to (e.g., el doctor, la doctora).
1. (bank thief)
a. bank robber 
Los atracadores llevaban medias en la cara para que no pudieran reconocerlos.The bank robbers wore pantyhose over their faces to avoid being recognized.
b. raider 
El atracador aceptó liberar a todos los rehenes si lo dejaban escapar con el dinero.The raider accepted to release all the hostages if he was allowed to escape with the money.
a. mugger 
Agente, vengo a denunciar que un atracador me ha robado la cartera a punta de pistola.Officer, I'm here to report that a mugger who robbed me of my wallet at gunpoint.