Full name of this file format is Rich Text Format, which means, that it is document format of Microsoft company. He was developed for Microsoft Word, because they were trying to create file type usable in all operating systems. Today isn´t this format used anymore, he was replaced by the newest file formats for Microsoft Office Word, they were se called .docx. He was developed and edited for a long period of time.
First version was done in 1987, but the reader of this format was done in Microsoft Word 3 for Macintosh. The creators were Richard Brodie, Charles Simonyi and David Luebbert. He was developed until 2008 to version 1.9.1, where XML elements were added. That was done due to ability to use HTML, later on the locking system was added and even more things.
He was usebla also in Office Outlook, where RTF e-mails can be created. He´s almost not used anymore, the main cause is probably because Microsoft Office 2010 can´t save files in this file type. This also counts for Microsoft Office 2013.