Self is the ruler.

Mantra 17

sarvendriyaguṇābhāsaṃ sarvendriyavivarjitaṃ /
sarvasya prabhum īśānaṃ sarvasya śaraṇaṃ suhṛt // 3.17 //

Himself devoid of senses, He shines through the functions of the senses. He is the capable ruler of all; He is the refuge of all. He is great.

~ Svetasvatara Upanishad – Chapter 3
The Highest Reality

✓ Sri T.N.Sethumadhavan has kindly explained thus:

The 1st line of this Mantra occurs in the Bhagavad Gita (13.15) which is quoted below.

sarvendriyagunaabhaasam sarvendriyavivarjitam
asaktam sarvabhricchaiva nirgunam gunabhoktru cha // 13.15 //

Shining by the functions of all the senses, yet without the senses, unattached, yet
supporting all, devoid of qualities, yet their experiencer.

The Self in us functioning through the sense organs looks as though It possesses all sense organs. But the sense organs decay and perish while the Consciousness which functions through them and which provides each of them with its own individual faculty is Eternal and Changeless just as electricity is not the light in the bulb and yet when it functions through the bulb it looks as if it were light.

The relationship of refuge or support of all can be explained as follows.

Waves are not the ocean but the ocean supports all the waves in as much as there can be no waves without the ocean.

Cotton is in the cloth but cloth is not the cotton. But it is the cotton in the cloth that supports the cloth. Similarly the world of plurality is not the Consciousness but it is the Consciousness that supports the world of multiplicities.

The influences which govern the human minds are called Gunas or Qualities.
They are
Sattwa (Unactivity), Rajas (Activity) and Tamas (Inactivity).

A live mind alone can experience these influences. But Life is the illuminator of these influences. Thus Consciousness conditioned by the mind is Jiva, the Ego and that is the experiencer of the Gunas.

Unconditioned by the mind, Consciousness in itself is
`Its own nature’, `It is the Absolute’.

Thus the Self, the Absolute, is beyond sense organs, mind and intellect, detached from everything and without any relation to the various Gunas.

But the same Self conditioned by the sense organs looks as though It possess all these sense organs, It is the sustainer of  them all and It is the experiencer of all the Gunas.

Hence this Mantra describes the Self as a capable Ruler of all and that He is great.