Career
In 1955, he took 4th in San Benedetto del Tronto. Keller beat Robert James Fischer in their individual game there. In 1960, he took 2nd in Zurich.
In 1961, he tied for 1st-2nd with Carlos Guimard in Enschede.
In 1975, he tied for 1st-3rd in Zurich. He played for Switzerland in three Chess Olympiads.
In 1956, at fourth board in 12th Olympiad in Moscow (+5 –5 =6);
In 1958, at third board in 13th Olympiad in Munich (+0 –1 =4);
In 1968, at first board in 18th Olympiad in Lugano (+4 –3 =7). Keller also played once in 1st World Team Chess Championship at Lucerne 1985 (+3 –2 =3).
He played for Switzerland in Clare Benedict Cup three times, 1958, 1960, and 1969.
Keller was awarded the International Master (IM) title in 1961. Efim Geller vs Dieter Keller, Moscow 1956, English, Symmetrical, A34, 0-1
Robert James Fischer vs Dieter, Zürich 1959, Ruy Lopez, Closed, C92, 0-1
Bent Larsen vs Dieter Keller, Zürich 1961, Hungarian Opening, A00, 0-1.