In Islam, a wali is a legal guardian or protector who has authority or guardianship over somebody else). In the context of marriage, a wali is a male guardian who plays a crucial role in the marriage process. The walis role is to ensure the well-being of the woman in all aspects of her life before and during the marriage process. The wali must give consent for the marriage to take place, and his presence is necessary for the nikah (marriage) of an adult woman to be valid).

By default, the father of the bride is her wali, but if he is not available, the role of the wali is usually taken on by the next closest mahram, such as the grandfather, son, grandson, brother, paternal half-brother, or paternal uncle. If none of these relatives are available, then the Islamic authority appointed by the ruler or judge would appoint a wali for her.

It is important to note that a woman may not take another woman as her wali. The majority of scholars agree that the wali must be a Muslim. In the Hanafi school of fiqh, there is a distinction between a wali ijbar and a wali ikhtiyar. A wali ikhtiyar does not have the authority to force and cannot arrange a marriage without the brides permission).

In summary, a wali in Islam is a legal guardian or protector who plays a crucial role in the marriage process. The walis role is to ensure the well-being of the woman in all aspects of her life before and during the marriage process. The father of the bride is the default wali, but if he is not available, the role is taken on by the next closest mahram. The wali must give consent for the marriage to take place, and his presence is necessary for the nikah of an adult woman to be valid.