He started showing himself to humans to see how they reacted, and the reactions usually fell into three categories: awe, desire, and friendly. How they treated each other and the Pokemon that were around them varied person by person, and while the ones who abused their positions of power angered him, he didn't interfere very often. He took to watching them from a distance and it amazed him how diverse they were despite having the same basic appearance.
They weren't physically powerful nor did they possess powers like Pokemon, but they were incredibly intelligent and could manipulate the areas around them to suit their needs. The bipedal creatures that weren't Pokemon in particular caught his attention. Raikou was the beast of electricity, and while running the region was one of his favorite past times, he started getting bored and curious of the other beings that dwelled in his region. Then the three beasts took to the wind, following no set path, but roaming the region of Johto as they pleased. Afterwards, Ho-oh brought the three Pokemon back to life, and supposedly the three creatures represented forces of nature surrounding the tower's burning. After lighting struck one of the towers of Ecruteak, a fire raged and killed three Pokemon inside, and a rainstorm came and put the fire out.
The legend of Ho-oh and the legendary beasts is simple. Pressure: The Pokémon raises opposing Pokémon's PP usage Soul Silver: A Pokémon that races across the land while barking a cry that sounds like crashing thunder.