Elden Ring centers around the Greater Will and, by extension, the 
Elden Beast. As an Outer God, the Greater Will has a hierarchy of servants to aid it in its plots to gain and maintain power over the Lands Between. While the Two Fingers play a large role in communicating directly with and relaying the will of the Greater Will, the Elden Beast has an even more important role.
[Warning: This article contains spoilers for Elden Ring.]
Elden Ring is set in the Lands Between, a place that is ruled by Queen Marika and her Golden Order. When the Tarnished Champion returns from their exile to the Lands Between, Queen Marika has already been imprisoned in the Erdtree for shattering the Elden Ring. The Tarnished follows Grace in the Lands Between to search for a way to repair the Elden Ring and either restore the Golden Order, or usher in a new age.
The Elden Beast is non-optional and the final boss fight in Elden Ring. It's said that the Elden Beast was contained within a star that the Greater Will sent to the Lands Between, and it would then become the Elden Ring. When Marika was chosen to ascend to godhood and become the vessel of the Elden Ring, she had to become one with the Elden Beast in order to be the vessel for the Elden Ring.
The Elden Beast Is A Vassal For The Greater Will In Elden Ring
Instead of going to the Lands Between itself, the Greater Will sent a vassal and envoys in its place. A vassal rules over a section of land in place of the land's owner, so the Elden Beast acts as the Greater Will's proxy in the Lands Between to carry out its wishes, making it the embodiment of order. The strongest Elden Ring sorcery originates from the Greater Will, and this is thanks to the influence of the Greater Will being spread because of the Elden Beast and the Two Fingers. Because it turns into the Elden Ring, then turns back into a beast to fight when the vessel is destroyed, the Elden Beast is, above all, an extension of the Greater Will.
The Greater Will's interference in the Lands Between is perceived as either a blessing or a curse depending upon who is asked. Though the Elden Beast bringing the Elden Ring and Grace to the Lands Between ushered in a golden age, but it didn't last, and Marika shattering the Elden Ring brought a devastating war to the Lands Between as the demigods fought for power. Despite their influence in the Lands Between, very little is known about the Outer Gods and those who enact their will, such as the Elden Beast, in Elden Ring.
