It's tricky to say exactly when dwarf planets were "discovered" because the definition of a dwarf planet is relatively new.

Here's a breakdown:

* Ceres: Discovered in 1801, originally classified as a planet, then an asteroid, and finally designated a dwarf planet in 2006.

* Pluto: Discovered in 1930, considered a planet for 76 years before being reclassified as a dwarf planet in 2006.

* Eris: Discovered in 2005, initially considered a "tenth planet" but then classified as a dwarf planet alongside Pluto in 2006.

* Makemake and Haumea: Both discovered in 2005 and officially classified as dwarf planets in 2008.

The concept of a "dwarf planet" itself was only established in 2006 by the International Astronomical Union (IAU). This means that before then, these objects were classified differently.

Therefore, it's more accurate to say that dwarf planets were recognized as a distinct category in 2006, while their individual discoveries happened at various points in time.