God (all Three Persons) has always existed, exists today, and will always exist. God was not created by any other entity. He is pure Spirit, outside of time and space. He is not capable of producing evil, He is pure Goodness, Light, and Love. Pretty mind-boggling, when you think of it. The evil you see is not caused by God–He only permits it to occur.
Satan, on the other hand, is a creature, like all angels (Satan is a fallen angel.) He has considerable power only because God permits it. Satan’s power, however, is limited, and he exercises it because he wants to see all humans as miserable and hateful as he is.
Being an angel, with intellect and will far superior to that of humans, Satan, as well as all the other angels, got one shot at deciding whether they would be obedient to God or to rebel against Him. Satan and the rest of the demons have absolutely no hope of redemption. They made their choice, and they are stuck with it. They are beyond salvation. Christ did not shed His blood for them. So we humans, in this sense, are far more graced than angels, because we can repent and have the assurance of redemption provided we want it.
Eventually, when God wills it, He will permanently kick Satan’s you-know-what, and Satan knows it. He just wants to take down as many of us as possible with him before that happens, because he is permanently deluded that his power approaches that of God.