Simplify the following text for a Grade 2 native English-speaking person.
Original: Ukko 's weapon was a hammer called Ukonvasara ( Ukko 's Hammer ) , or an axe or a sword , by which he struck lightning ( see thunderbolt ) .
Simplified: Ukko was an old man and he lived on the sky . He had a weapon - hammer or axe called Ukonvasara .