Father of the Bride
If he is hosting the wedding with the bride's mother, then he is usually aware of the arrangements and may choose to participate in some aspects of the organisation.
On the day, he and the bride have a little time alone before travelling together to the ceremony. He accompanies her in the wedding car to the ceremony, and walks her down the aisle on his right arm.
When the vicar/registrar asks 'who is giving this woman to this man?', he takes the bride's right hand and places it in the officiant's.
He sits to the left of the aisle, usually with the mother of the bride, and attends the signing of the register.
He takes the bridegroom's mother on his right arm, and escorts her down the aisle during the recessional.
If he is co-hosting the reception, he welcomes guests. Traditionally, the father of the bride delivers his speech first.