Who was the first champion in LoL lore? And why was he chosen to be?

Chronologically in the lore or who did Riot first write lore for?

Be more specific

Well and were the first champs designed, if that's what you mean. So in theory they would be the first ones in the lore.

Yordles exist in another dimension outside of time and space. For example, Fizz showed up on Runeterrra before Targon did, because he wanted to play with the mortals from the other dimension... The mortals at the time happened to be fish people, because Targon did not create humans yet.

Kindred, Bard or Aurelion Sol. Yordles and other spirits and a close second.