Graham Hill is the only driver to have won the Triple Crown (under either definition). He won Le Mans in 1972, the Indy 500 in 1966 and two F1 world championships.
Jim Clark has a BTCC Championship to his name in 1966, two world championships and the 1965 Indy 500.
Jacky Ickx has six Le Mans victories to his name, the 1983 Paris-Dakar, 1977 Bathurst 1000, 1966 Spa 24 Hours, 1979 Can-Am Championship and his 8 GP victories are nothing to be sneezed at (he came close to a championship though).