Who actually caught them all?

[Mr Khan]

I did with Pokemon Blue, but only through massive cheating

A three-point cheating plan

1: Get by with a little help from my friends, who were better at the game and got stuff without cheating. Also necessary for those that didn't exist in Blue.

2: Infinite Master Balls (via Missingno. glitch)

3: Get Safari Zone pokemon to appear outside the zone (also via the missingno. glitch. Basically just enter the zone, leave quickly, then fly to Cinnabar Island and surf up and down, and all the pokemon from the region would appear there, but you could apply normal items to them)