Creon is arguably the most tragic figure in Antigone, going from a powerful king to a man bereaved of everyone he ever loved due to his own arrogance. His tragic flaw is his pride, which makes him believe he can defy the will of the gods and basic decency towards his fellow human beings.
Creon's pride is what inspires him to pass unjust laws regarding the body of Polynices, Antigone's brother. After trying to depose his brother Eteocles when he would not step down from the throne after the allotted period, Polynices revolted, only for both brothers to end up dead. Creon orders that Polynices not be buried properly, thus dooming his soul to never find the afterlife. Antigone rebels against this cruel decree, burying her brother properly.
Creon's pride prevents him from seeing how both his law and his attempt to do "justice" by executing Antigone are unnecessary and cruel. He thinks only of the need for order within the state. He is willing to do whatever he believes it takes to make everyone remain at peace, even though this means hurting the people he loves, including his own son, who is in love with Antigone and certainly does not want her killed. In the end, Creon sees his mistakes for what they are too late, and his pride isolates him from everyone he once loved, leaving him only with the emptiness of power.