Tras
With tras (after, behind) you can specify location and time. The location indicates that something is behind an object, a person:
La pelota está tras el sofá.
However, the prepositional expression detrás de is used more frequently:
La pelota está detrás del sofá.
In the case of time specifications, tras is used to express that something happened after an event. It can also be used by después de:
Tras su operación cambió mucho.
Después de su operación cambió mucho.