Who was the English Knight Templar holding command in the Mongol Army?

Question

Excerpt from Great Captains Unveiled (1927), by B. H. Liddell Hart:

After this holocaust, Hungary was occupied without further fighting. An organised administration was set up, and the land settled down under its new conquerors. There was no attempt to push farther into Europe, apart from one reconnaissance into Austria, which, strangely enough, was carried out under an English Knight Templar who held command in the Mongol Army.

This is taken from the Genghis Khan and Subutai chapter (bold is mine), right after the Battle of Legnica, where the Mongols defeated Poles, Moravians, and Templar Knights.

In the same book (in fact just before the text I quoted) Hart says "the Knights Templars die fighting to the last man".

Who was this Templar knight?

Answer 1

As interesting as this seems to be, there seems to be not much light available to shine onto this issue, except for the fact that such a man existed, although probably not really in command of that late and lonely mission:

Among eight Mongol prisoners captured in Austria during this reconnaissance there was an Englishman. He had once been a Templar, but after being banished from England for an unknown crime, he had travelled through the Middle East and entered the Mongol service as an interpreter. It was said that he spoke seven languages. Matthew Paris mistakenly records that it was this Englishman who delivered the letter to King Bela which was in fact intercepted by Friar Julian, and some say that he was in com­mand of the reconnaissance force, but this is unlikely since such a command would not have been given to anyone other than a Mongol. The only certainty seems to be that among the many nationalities in the Mongol corps of interpreters there was at least one mysterious Englishman.
_{— James Chambers: "The Devil’s Horsemen. The Mongol Invasion of Europe", Book Club: London, Edinburgh, 1979, p 110–11.}

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If there ever was to put a name on it, or him, shaky evidence points to an almost legendary figure, note the surname, of Robert Eracles (Hercules):

Tartar Khan's Englishman (i.e. the book mentioned in Twelfth's answer) [speculates] that the Englishman had probably been Master Robert Eracles––an English knight and former advisor to King John who had been exiled and eventually picked up by Mongol talent scouts and taken to Mongolia.
_{— Tim Cope: "On the Trail of Genghis Khan: An Epic Journey Through the Land of the Nomads", A&C Black, 2013, p474.}

Master Robert Eracles was an English knight who was present at Runnymede for the signing of the Magna Carta. He thereafter journeyed from the Middle East to Mongolia in 1243, whereupon Genghis Khan enlisted the linguistically talented Eracles as a diplomat. The knight turned Long Rider then rode from Central Asia back to Europe, where he was beheaded by Europeans for having assisted the Mongols.
_{— Historical Long Riders}

Both these accounts are not hard evidence and depend on the overly optimistic reconstruction made by Ronay. This is deemed not impossible but "conceivable".
_{Cf. — Felicitas Schmieder: "Europa und die Fremden. Die Mongolen im Urteil des Abendlandes vom 13. bis in das 15. Jahrhundert", Jan Thorbecke: Stuttgart, 1994, p54. (worldcat/academia.edu)}

Answer 2

I've never seen the reference to the 'Templar' portion in particular, but an Englishman in the Mongol horde is something I've read. Unfortunately I can't find the book itself and simply have a review of the book to point to: The Tartar Khan's Englishman

Ronay's deductions are sound and his theory for the identity of the Englishman is very believable and well-supported by evidence. However, there are so few facts to work with and the truth can most likely never be proven at this point. I had to be cautious while reading to distinguish his asserted facts and his suppositions, because they are often written the same way and some of the things he says don't seem to be based on evidence at all (he doesn't really do textual citations). But regardless of whether every fact is correct, this peculiar story is true, there really was an Englishman who joined the Mongol invasion of Europe in the 13th century. And whether Ronay has finally put the right name to this incredible character or not, he does an amazing job describing the backgrounds the Englishman would have recognized, educating the reader on political issues and what life was like in 13th century England, the Middle East, and Asia.

One of the theories (although contested) on why the Mongols never pushed further into Europe was that the Great Khan Ögedei's death prompted the return of the Mongol leadership to Mongolia to elect a new leader (Rus uprisings being another potential). In the leadership void that this left, there is a potential for an Englishman general to have marched at the head of a Mongol horde.

Unfortunately this is all still hard to prove and it's all speculation.

Answer 3

According to Mergers, Acquisitions and Global Empires: Tolerance, Diversity and the Success of M&A it was a Knight Templar named Robert, who had been kicked out of England:

The Mongols even employed an Englishman by the name of Robert, who was in their services for almost 20 years before being captured by Austrians during a raiding mission in the Vienna Woods. Robert was a former Knight Templar who later found employment as an interpreter for the Mongols...

(seems to be the same individual mentioned by LangLangCs answer...)