Question

were they in existance before people in the poke planet or they are alien life forms?

Answer 1

http://bulbapedia.bulbagarden.net/wiki/Timeline_of_events_in_the_anime this timeline should answer your question

Comments

i asked where did they came from ,not how did they created and when...

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They were created by arceus they didn't come from anywhere 0_o

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"were they in existance before people in the poke planet"
Seems to be asking for a when there.