In this regard, two oft-quoted verses from the Psalms are as follows:
The fool has said in his heart, "There is no God." They are corrupt, they have committed abominable deeds; There is no one who does good (Psalm 14:1 NAS).
The fool has said in his heart, "There is no God," They are corrupt, and have committed abominable injustice; There is no one who does good (Psalm 53:1 NAS).
While not exactly synonymous with the sentence "God is dead," the sentence "There is no God" are almost equivalent, practically speaking. When the psalmist, David, wrote these words, a significant number of the world's people at that time did not believe in one God, as the Hebrews did; rather, they believed in a multiplicity of gods (with a lower case G). Moreover, they would make fun of a Hebrew who believed in the One True God by taunting him, saying
"Where is your God?" (Psalm 42:3 and 10).
In other words, where is your god's idol; that is, one carved out of wood or stone or cast in metal? "Who ever heard of an invisible God?" they would ask.
Moreover, the "fool" in Psalms 14 and 53 is not a fool in the modern sense of being a clown, or a court jester, a doofus, or a comedian; rather, a fool in the biblical sense is someone who acts foolishly by disregarding and even disparaging the wise counsel of his parents or other responsible and moral role models and authority figures. The book of Proverbs describes the fool in this sense very well (see, for example, 7:22; 10:8, 10, 18, and 23; 12:15 and 16; 13:16; 14:7 and 16; 15:5; 17:7, 10, 12, 16, 21, 24, and 28; 18:2, 6, and 7; 19:1 and 10; 20:3; 23:9; 24:7; 26:1, 4, 5, 6, 8, 10, 11, and 12; 27:3; 28:26; 29:20; and 30:22).
Combining these two thoughts, the fool who says in his heart there is no God is in effect saying,
"There is no God for me!"
In other words, the fool says,
I am an autonomous person, and I am my own authority.
I am going to do whatever I feel is right, even if everyone says it's wrong.
I'm going to live according to my rules, not the rules of my parents, the rules of society, or the rules of law enforcement (i.e., cops, judges, courts).
In one of Jesus' parables, we read the following words,
But God said unto him, "Thou fool, this night thy soul shall be required of thee: then whose shall those things be, which thou hast provided?" (Luke 12:20 KJV).
This fool was proud of his accomplishments in making a comfortable life for himself, and he determined to make his life even more comfortable by increasing his earning potential, not realizing he was going to have a massive heart attack and God was going to end his life.
Brilliant men and women down through the ages have been fools by disregarding and disparaging the evidences for God's existence which reside in the human heart and in the marvelously and staggeringly complex universe in which we reside (see Romans 1:20-23; and 2:14-15, quoted below). They may appreciate the finer things in life and marvel at the beauty which exists everywhere around them, but they eschew at all cost being held accountable by a holy and righteous (yet merciful and loving) God. In addition to being spiritually dead (as all Christians were at one time), they are blind spiritually, and willfully so.
"(Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law, since they show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts now accusing, now even defending them.)"
"For since the creation of the world God's invisible qualities--his eternal power and divine nature--have been clearly seen, being understood from what has been made, so that men are without excuse. For although they knew God, they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened. Although they claimed to be wise, they became fools and exchanged the glory of the immortal God for images made to look like mortal man and birds and animals and reptiles" (my italics).
Although radical Darwinists and macro-evolutionists would deny being idol worshipers, they are in fact just that. To them, the animal kingdom, including the human animal, is the ultimate reality which began in the primordial ooze. Over time ("billions and billions of years") that primitive slime evolved into advanced and highly complex forms of life by accident via successive and small beneficial variations (i.e., genetic mutations). Who needs God, when the cosmos is all there is and all there ever will be?