Romilly was a physicist and astronaut participating in the Endurance mission through the wormhole.
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.
This interstellar character was made using a Cooper figure as base. Two different heads was sculpted, one with his helmet and other without it. Regards.