Tramp development started at the end of November 1998 as rssh.el. It provided only one method of access. It used ssh for login and scp to transfer file contents. The name was changed to rcp.el before it got its present name Tramp. New methods of remote access were added, so was support for version control.
April 2000 was the first time when multi-hop methods were added. In July 2002, Tramp unified file names with Ange FTP. In July 2004, proxy hosts replaced multi-hop methods. Running commands on remote hosts was introduced in December 2005. Support for gateways since April 2007 (and removed in December 2016). GVFS integration started in February 2009. Remote commands on MS Windows hosts since September 2011. Ad-hoc multi-hop methods (with a changed syntax) re-enabled in November 2011. In November 2012, added Juergen Hoetzel's tramp-adb.el.
XEmacs support was stopped in January 2016. Since March 2017, Tramp syntax mandates a method.