Answer to https://pokemondb.net/pokebase/308641/

This answer is missing LGPE information. If you're not okay with this, then just tell me, and I'll convert my answer to a comment.
RBY: rival (as champion)
GSC: Red
RS: Steven
FRLG: rival (after Sevii Islands)
E: Wallace
DP: Cynthia
Pt: Cynthia (after Stark Mountain)
HGSS: Red
BW: tie, Alder and Cynthia
BW2: Benga
XY: Diantha (Black Writ)
ORAS: Steven
SM: Red
USM: Giovanni
[source][1]
[source][2]


  [1]: https://pokemondb.net/pokebase/302047/
  [2]: https://bulbapedia.bulbagarden.net/wiki/Prize_money