Advanced reptilian aliens, inhabitants of the planet Draconia, who ruled a vast space empire, but whose Empire suffered a terrible plague during the twenty-first century.  The Doctor was able to find a solution to the problem, and was made a noble of the Court of Draconia. 

It was around five hundred years later, when men came into contact with the Draconians during the 24^th or 25^th Century, when the Draconian and Earth Empires had expanded so much that there were minor incursions and petty squabbles, conflicts between Earth and the Draconians about their respective areas of colonization began to erupt as Earth’s influence grew. 

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A diplomatic mission was set up to sort these out but an ion storm damaged both ships.  As a result of the misunderstanding, a major conflict was started by General Williams. who was in control of the Earth ship which attacked and destroyed the Draconian one. 

A terrible war followed, costing millions of lives on both sides, until a peace was negotiated.   For the next twenty years, a delicate cold war existed between the two Empires, despite the creation of a frontier in space over which neither side could transgress. 

The Twenty year peace came to an end when, the Daleks engaged the services of the Master and even offered the use of their Ogron slaves, to try to foment a war between Earth and the Draconians. 

The plan almost worked as the Draconians horrified to discover that humans were making attacks on their freighters on their side of the border, and the humans counter argued that the Draconians were doing the same to Earth cargo ships came very close to starting another war.  But the Master’s schemes were ultimately exposed and thwarted by the Third Doctor, who convinced the two Empires that a third party, was trying to provoke the war (QQQ).

After the revelation of the Master's plan and the discovery of the existence of a 10,000 Dalek army poised to attack the Alliance on Spiridon, the Draconians teamed up with Earth and the Thals to strike back at the Daleks (SSS). 

After they fought beside them in the Alliance during the Second Dalek, Third Dalek, and Cyber Wars of the 25^th and 26^th Century, the Draconian Empire, found its resources depleted, and was unable to compete with Earth. They then entered into a long period of stagnation.