waaay back when the elders were introduced, their first story as collective was the grandmaster's plan to kill off galactus and restart the universe which would give all of them a portion of the power galactus wielded split amongst them all. they also had a grudge against him since he was older than them, he's an elder just not a part of the "brotherhood" the elders of the universe
surfer and mantis were spying on them at their meeting place, the elders were then alerted to them by ego who was actually the planet they were on in disguise. he was revealed to be an elder himself, who was going to take part in killing galactus.