Death is certain. It comes to everybody except to those stated in the bible. But where and when did Death come to the world. Is it a natural phenomenon or something like a curse?
The Bible teaches that death entered into the world because of Adam's sin:
Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned— To be sure, sin was in the world before the law was given, but sin is not charged against anyone’s account where there is no law. Nevertheless, death reigned from the time of Adam to the time of Moses, even over those who did not sin by breaking a command, as did Adam, who is a pattern of the one to come. (Romans 5:12-14)
For since death came through a man, the resurrection of the dead comes also through a man. For as in Adam all die, so in Christ all will be made alive. (1 Corinthians 15:21-22)
There are debates over what type of death was involved in the fall. I believe that it was holistic death. It clearly involved spiritual death, as Adam was a sinner needing redemption. But earlier in 1 Corinthians 15 Paul says that if the resurrection we are hoping for isn't physical then our hope is in vain:
For if the dead are not raised, then Christ has not been raised either. And if Christ has not been raised, your faith is futile; you are still in your sins. Then those also who have fallen asleep in Christ are lost. If only for this life we have hope in Christ, we are of all people most to be pitied. (1 Corinthians 15:16-19)
The solution matches the problem, and so if it required the Son of God to be resurrected to give us life, then I believe that physical death is a result of sin too.
Is death natural or a curse? There's a very real sense in which it is natural. So I would say that death's naturalness is a curse. The curse changed the world from a world where death was unnatural to one where it is the most natural thing of all.
It is a pious opinion, fairly commonly held based of Romans 5:12 ("Sin came into the world through one man...") and Romans 6:23 ("The wages of sin is death...") that there was no death sin in the world until Adam committed the first sin. However, this ignores two facts: first, neither the condemnations pronounced by God against Adam (Genesis 3:17-19), or Eve (Genesis 3:16) mention either taking away physical immortality; second, in Genesis 3:22, the reason given for expelling Adam and Eve from the Garden of Eden is "lest he put forth his hand and take also of the tree of life, and eat, and live forever." If Adam were immortal to begin with, then the immortality would have had to have been taken away, and "lest he put forth..." would have been unnecessary.
Further, some of the smallest aquatic creatures created on day 5 would have had to have eaten before Adam's creation on 6, and they would have consumed other creatures, since the smallest creatures have to eat almost constantly to maintain enough energy to survive, killing them in the process.
So evidence from the Bible supports that death was part of creation from the beginning, both for other creatures, and for humans.