Romilly was very fearful of space travel and is bothered by the concept that only a few millimeters of bulkhead separate himself and his fellow astronauts from the vacuum of space.
Romilly is portrayed by British actor David Gyasi.
Romilly was among the scientists who briefed Cooper on the discovery of the wormhole near Saturn.
After Cooper starts spinning the Endurance, Romilly asks for his medication from Brand.
While at Saturn, Cooper goes to Romilly and talks to him. Romilly says that he cannot stand the fact that there only millimeters of aluminum lie between him and the vacuum of space. Cooper cheers him up by saying that they are explorers, and the Endurance is their boat. Cooper then gives him earbuds so Romilly can listen to the sounds of nature.
When near the wormhole, Romilly erupts in excitement as he is finally seeing the wormhole up close. Cooper asks how a wormhole works, so Romilly explains it for him.
After arriving at the Gargantua system, Romilly opts to remain onboard Endurance with TARS while Cooper, Brand, Doyle and CASE recover Dr. Miller and her data on Miller. He intended to benefit from the Endurance's proximity to Gargantua to study the black hole and gather as much information as he could to help Dr. Brand with his equation.
The immense time slippage from the Gargantua black hole causes 23 years, 4 months and 8 days to pass while Cooper and Brand are on Miller's. Although Romilly does use the hyper-sleep chambers a few times to catch up to their return, he mentions to Brand that he "did not want to dream his life away", indicating he spent some of the time active on the ship, enough to demonstrate the age evidenced by his appearance.
In an emotional conflict with Brand, Romilly decides to side with Cooper on inspecting Mann's planet.
On Mann's, Romilly was killed in an explosion caused by Dr. Mann while accessing KIPP's archive; which contained the true data of the planet. TARS escaped the explosion and was able to rejoin the rest of the crew in the lander.