4: Agni, the God of Fire in the Veda; the oldest and the most revered of the Gods in India.  He is the triple aspect of Fire and therefore the sum total of manifestation.  He is regarded also as the Lord of the mental plane (the 5th plane) whose symbol is Fire.
Varuna, the God of Water, in the sense of the waters of space, or the waters of matter.  He is regarded also as the Ruler of the astral plane (the 6th plane) whose symbol is water.
Kshiti, the God of the Earth in the sense of dense substance, and not a planetary body; he is the God of the physical plane, the seventh plane.