Are Mclaren and Mercedes the only constructors to have won the triple crown (Le Mans/Indianapolis 500/Monaco GP) of motorsports?
Le Mans 24: 1995
Indianapolis 500: 1974, 1974
Monaco Grand Prix: 15x between1984 and 2008
Le Mans: 1952/1989
Indianapolis 500: 1915
Monaco Grand Prix: 1935/1936/1937
There are a few historic names who have won a couple of the three, but in a quick browse of the history
books wiki pages I can’t add to Mclaren and Mercedes:
+Ferrari have won in Monaco 8 times, and le Mans 9 times, but have never won the Indy 500.
+Renault won le Mans in the 1970s and have won in Monaco but have no Indy 500 victory.
+Peugeot won the Indy 500 in the 1910s – twice – and have had 3 more recent le Mans successes, but no Monaco Grand Prix wins.
+Team Lotus and Maserati have no le Mans victories.
Ford have won le Mans outright, but their Monaco and Indy 500 wins came as an engine manufacturer to other constructors.