Robert Downey Jr. wears an Urwerk UR-105CT

In Avengers: Endgame (2019), the watch shows up in the quiet scenes at the Avengers compound. Tony Stark stands with his arms folded, glasses on, a dark cardigan pushed up his forearms, and on his left wrist sits a low, rounded hump of bright metal, ribbed across its top like the cladding of an old streamline locomotive. In the wider shots, where the team gathers in the compound lounge, the same case is there under his sleeve.

It is an Urwerk UR-105 CT Iron, and the way it got onto that wrist is unusual for a franchise this size. Urwerk does not pay for product placement. The watches arrived because Robert Downey Jr. asked for them: during the filming of Spider-Man: Homecoming he requested a UR-110 in rose gold, believing the brand fit Tony Stark, and the relationship carried on into Endgame with the UR-105 CT.

Urwerk is a small Geneva company, founded in 1997 by the watchmaker Felix Baumgartner and the designer Martin Frei, and the UR-105 CT was its twentieth anniversary piece, launched in 2017. The case is titanium and polished steel, and its upper surface is a hinged hood: slide the catch at the top and the hood lifts to expose the works. Underneath, four satellites, each carrying three hour numerals, swing in turn past a curved minute scale, so the hour you read is always the one crossing the track. Frei has said the design drew on New York, where he lived for years, on Art Deco, and on the optimism about technology that the streamline era put into its trains and ocean liners. On the back, two small turbines govern the automatic winding, and the wearer can set them to run free, damped, or locked.

Downey kept the brand on after the cameras stopped. At the Los Angeles premiere on April 22, 2019, he wore another Urwerk, the UR-111C. The watches he had worn were then sold for charity one by one, and by 2021 the run of RDJ Urwerks had raised more than 700,000 dollars at auction.