"Created" is when the file was created on that particular filesystem; e.g. if you just copied a year old file from another drive, or extracted from an old archive, the new copy will be "created" today. As far as I know, there is no function to "backdate" this timestamp. So this is the one you're looking for.
"Modified" is when the file was changed anywhere. This timestamp is generally copied around along with the file – even things like archivers, web browsers, and FTP often preserve it. So, very often, it reflects the original file modification time. (On the other hand, it's easy to accidentally reset it...)