Indra is the lord of the ten sensory perceptions, Indriyas.

Jnanendriya, perception: seeing, hearing, smelling, tasting, touching.
Karmendriya, action: speaking, grasping, walking, excrete, procreate.

Because of a curse Indra is always worried about his throne, worried about being conquered. He then sends an apsara to the ascetic who has immersed himself in tapas to disturb him.

He also works for us. When we go into meditation, want to calm our sensory perceptions, want to bring them under control instead of being their slaves, then Indra rebels. The mind does not want to be ‚conquered‘, it wants to let the senses run free. That is why it is so difficult for us to find peace in meditation. Indra does everything possible to disturb the meditator.