It looks like Edwin Moses is about to have company:
Eliud Kipchoge: bronze in the 5,000 in Athens in 2004. He's likely to win a medal in the marathon in Rio.
Ezekial Kemboi: gold in 2004 in the steeplechase. He's likely to win a medal in the steeplechase in Rio.
Is there anyone else in this club or about to join this club? (Bernard Lagat is a long shot.)
That brings me to another question. Which runners have competed in the same event over four Olympics? To my knowledge, it is only:
Emiel Puttemans: 5,000 meters (1968-1980).
Johnny Gray, 800 meters (1984-1996).
Haile Gebrselaisse: 10,000 meters (1996-2008).
Edwin Moses would be in this group were it not for the US boycott of the Moscow Olympics.
But also worth noting are:
Gaston Roelants: 1960, 4th in steeplechase; 1964, 1st in steeplechase; 1968, 7th in steeplechase, 11th in marathon; 1972, dnf in marathon.
Francie Larrieu-Smith: 1972, 1,500 meters (8th in semifinal heat); 1976, 1500 meters (9th in semifinal heat); 1980, made US team in the 10,000 meters; 1988, 5th in 10,000 meters; 1992, 12th in the marathon.
Al Oerter won a gold medal in the discus four times. But he's not a "runner."