I've been watching a series of renown biopics called Drunk History, one episode of which claims that Alexander Graham Bell stole the design for the telephone from Elisha Gray.
Is this speculation or fact? What evidence exists?
I've done some Wikipedia and Google research but I'm still unclear.
In regard to the controversy between Elisha Gray and Alexander Graham Bell, there are lots of claims but almost no actual evidence to support the idea that Bell stole the design for the telephone from Elisha Gray. It is worth reading the Wikipedia article on the controversy.
The weight of the evidence - in particular the evidence that Bell had been using liquid transmitters in experiments more than 3 years before filing his patent - supports the idea that Bell came up with his design entirely independently of Elisha Gray.
In the interests of completeness, I suppose it is also worth mentioning that a 2002 resolution by the US House of Representatives (House Resolution 269) acknowledged the role of the Italian inventor Antonio Meucci in the development of the telephone (although it stopped short of crediting him with its invention).
Although widely (and inaccurately) reported, House Resolution 269 has also been widely criticised for its factual errors, inaccuracies, biases and distortions, for example in Intellectual Property Law for Engineers and Scientists by Howard B. Rockman.
In response to the bill passed by the US House of Representatives, the Canadian government passed a similar motion declaring Alexander Graham Bell to be the inventor of the telephone.
Politicians will be politicians, right?
Either way, this had no bearing on the controversy between Elisha Gray and Alexander Bell.
After an extensive edit, this is probably a long comment rather than answer.
Bell's design was developed independently from Gray's, and probably from Meucci's. This article of The Guardian uses the verb "steal", but quoting @sempaiscuba, TG is no stranger to controversy.
Many "respectable" articles claim that he conducted experiments in the same laboratory where Meucci's materials "had been stored by Western Union", but in fact he had sent descriptions and drawings to Edward Grant of the American District Telegraph Company in New York.
Undoubtedly, Meucci is a father of the telehone and this was implied in House Resolution 269 by the US House of Representatives in 2002, though not explicitly stated. In its words, if Meucci had been able to pay the $10 fee to maintain the caveat after 1874, no patent could have been issued to Bell. As a matter of fact, HR269 was criticised.
An early verdict stated that Meucci's design was mechanical and not electrical. But according to Giovanni Schiavo, an Italian-American historian, this verdict is one of the most blatant judiciary mistakes in the annals of American justice. (After all, the device was called telettrofono, "telectrophone"). Meucci started to think of his design after some electrotherapy experiments in 1849.
It was in 1854 that he realized the first prototype of telephone, which he would call telettrofono. He used it to communicate from his laboratory with her wife, who was bedridden. Unfortunately he was quite poor, and couldn't afford to patent the invention. Only in 1871 he managed to have a patent caveat, i.e. a temporary patent, but he could renew it only until 1873.
I read there is doubt about this last aspect, because he patented other inventions from 1872 to 1876, costing $35 each, but I see nothing strange: who lent him the money for renewing the patent of the telettrofono stopped doing so in 1874, probably foreseeing no future advancement for Meucci, but this didn't stop other creditors from supporting other inventions of his.
