Your question, I think, has an incorrect supposition, in that gold "became a backer" of other currency. Gold has been used as money and currency since coinage was invented, and before that it was used in trade both in "raw" form and in the form of finished products. Gold does not tarnish or rust or "rot" like other metals, and is extremely ductile, and thus easily worked and drawn out. It is valuable for these properties as well as its relative scarcity.

The trend throughout modern history has been first to replace gold as currency with banknotes, as gold was at times considered "cumbersome", both for the practical reasons of carrying and storing it and also because the supply of gold cannot be inflated at will. At first, these notes were pegged to metals in order to represent claims to the physical money that people were accustomed to (hence the term backing), but more recently these notes exist simply as fiat paper. That said, gold is still money, even though it is rarely used as currency at present.

Valuations for gold were historically rather stable and based on its scarcity relative to silver, which was a much more common currency. This ratio was for millennia in the range of 12 or 15:1 by weight. Alexander's shipments of spoil from his campaign in the East altered the ratio with an influx of gold into the West. At later times, the ratios were set by government fixing. This could cause problems, for example, if other entities had different valuations or if large deposits of either metal were discovered. More recently the ratio has fluctuated much more wildly.

Gold and silver have alternated and often co-existed as monetary standards for perhaps 27 centuries, gold often being preferred for state reserves or large-scale trade (presumably in part because you needed only around a tenth of the weight), silver or other metals (copper and alloys) for everyday use (you could make lower-denomination coins). Europeans have tended to prefer gold when they could get their hands on it, Asians silver, perhaps because it's more useful.

That worked fine when Europe found itself with a windfall of tens of thousands of tons of silver in the centuries after 1492 (in fact starting three decades earlier with strikes in central Europe), using it to oil the wheels of commerce and pay for exotic imports from the east. In the 16th-19th centuries most of Europe effectively operated a bimetallic standard, with both silver and gold coins whose relative value varied with that of the two metals.

Sir Isaac Newton is commonly credited with establishing the modern gold standard by setting the golden Guinea at 21 silver shillings in 1717, overvaluing gold and driving silver out of circulation to be shipped abroad or melted down: in fact he seems rather to have failed to correct a half-century-old mismatch between the two units, whether by accident or design ("If things be let alone till silver money be a little scarcer, the Gold will fall of itself," he wrote).

Fortunately for Britain, gold became a good deal more readily available in the 18th century thanks to gold finds in Brazil and the special relationship with Portugal, and the country officially moved to gold in 1816. The US and Europe followed between the 1870s and 1890s, a move often seen as connected with the period's severe price depression: this time discoveries in South Africa, the Yukon and Alaska came to the rescue.

Suspended in most of Europe in 1914 and restored in modified form in the 1920s, the standard outlived its usefulness in another still deeper Depression this time with no Klondike in sight, being abandoned successively by the major players in 1931-36. While currencies resumed their link to gold after WW2 there would be no return to fixed rates, with devaluations aplenty until the agony was finally ended in the early 1970s.