The zeppelin bend was used extensively to anchor zeppelins to the ground. Sometimes called the Rosendahl Bend, it is used to join two lines together. This knot meets all the requirements in that it is easy to tie, won't jam even after repeated jerks or under a maximum load, remains easy to untie and is strong, secure, and symmetrical.
The zeppelin bend Is sometimes referred to as a Rosendahl Bend because Vice Admiral Rosendahl would only allow zeppelins under his command to be anchored using this particular knot. Considering zeppelins weighed 20 tons or more, that's saying a lot. Zeppelins are no longer in use so this particular knot has almost been forgotten.