Keeper of the Balance

"I went back and checked the archives for anything on the Mortis monolith."
"And?"
"I found confirmation in a report from Obi-Wan. It was just as Yoda told me. Obi-Wan seemed to think that he and Anakin had been drawn to Mortis because the Father was dying and he wanted Anakin Skywalker to take his place as the Keeper of the Balance."
"Chosen One indeed. What happened?"
"Obviously Anakin didn't accept, the Son ended up murdering the Daughter with a special Force-imbued dagger and the Father tricked the Son by sacrificing himself with the same dagger, so that Anakin could kill the Son."

―Luke Skywalker and Jaina Solo^[2]

The Keeper of the Balance was the role of the Father of the Ones. The Killiks of the Thuruht hive believed that Abeloth, as the "Bringer of Chaos," was the counterpart to the Father's role as the "Keeper of the Balance."^[2]

During the Clone Wars, the Father wanted the Chosen One, Anakin Skywalker, who was destined to bring balance to the Force, to replace him in his role as Keeper of the Balance. During the return of Abeloth in 44 ABY, Grand Master Luke Skywalker—the son of the Chosen One—read the mission report in the Jedi Archives about his father and his mentor's experiences on Mortis. Combined with the information gathered from the Thuruht hive, Luke realized that his father's refusal to become the new Keeper of the Balance had in fact set off a disastrous chain of events. With the death of the Ones, the galaxy began to slide into chaos; the number of conflicts in the last 65 years were evidence enough of that.^[2]