BY ANY OTHER NAME - A "STO-AWAY" IN MIDSOMER

From the TARDIS Data Core Wiki:
Mr. Copper was an employee aboard the Titanic who met the Tenth Doctor and Astrid Peth.  After the near-destruction of the vessel, the Doctor allowed him to live in 21st century England.  
(TV: Voyage of the Damned)

Mr. Copper was a travelling salesman, but he reached retirement with little to show for a life's work. He pretended to have a first-class degree in "Earthonomics" to get the job of Ship Historian. In reality, he had been a student at Mrs. Golightly's Happy Travelling University and Dry Cleaners.

Copper helped the Tenth Doctor defeat the Host. After this adventure, he was stranded on Earth with nothing save the clothes on his back and a million-pound credit card. He had been issued this by the Capricorn Cruise Lines for purchasing trinkets from the local life forms, including samples of their local delicacy, beef.

After being refused an opportunity to travel with the Doctor (because the Doctor did not want a new companion at the time), the Doctor told Copper that the credit card he had was worth the local equivalent of 50,000,056 credits. Ecstatic at his newfound wealth, he planned to make a life on Earth so he wouldn't spend the rest of his life in prison on Sto for fraud.

Mr. Copper eventually used some of his wealth to establish the Mr. Copper Foundation, an organization dedicated to advancements in science.  Among the Mr. Copper Foundation's creations was the Sub-Wave Network.
(TV: The Stolen Earth)

Copper's first name was unknown within the episode.  There are reports it was supposed to be Bayldon, but ultimately for Toobworld it is irrelevant.

The Titanic disaster occurred over two days – December 24-25, 2008, Christmas Eve and Christmas, 2008.  The episode was broadcast on Christmas Day, 2007.

Once the Mr. Copper Foundation was established and Mr. Copper had set up the hierarchy so that the foundation could run without his active participation, he withdrew from public life.  Taking the alias “Felix Hope”, he chose to live in Bleakridge, a village in Midsomer, the farthest one from Causton.  It was quite secluded, surrounded by moorlands.  

There he met an Earth woman named Cecily, and they soon married.  For the next decade, they lived a quiet, isolated life there in Bleakridge, with Cecily never the wiser that “Felix” was an alien.  (Humanoids from the planet Sto are basically indistinguishable from Terran humanoids.)

Their voluntary positions with the Bleakridge Village Watch was the most active Mr. Copper had been in Earth affairs since the Doctor dropped him off in 2008.  But that all came to an end when Causton C.I.D. showed up to investigate a series of murders.  Even so, nobody suspected that Felix was not of that Earth.  
(TV: ‘Midsomer Murders’ – “Crime and Punishment”)

As Sto humanoids are similar in genetic structure to the humans of Earth Prime-Time, so too are their lifespans.  Mr. Copper, AKA Felix Hope passed away in 2019; his wife Cecily – as of this writing – is still alive.  “Felix” left her comfortably provided for to see her through to her own final days.  But the majority of his fortune, which had been invested wisely over that decade, was used to keep the Mr. Copper Foundation in operation.