Based on the Bhagavad-Gita, the living entity is the eternal soul and not the body which is temporary. So basically we are the soul and not the body. The car and the driver are two different entities. In a similar way, the soul and body are two different entities, one is living (the soul) and the other is dead matter. Without the driver, the car is completely useless. In a similar way, without the soul, the body is completely useless.
“As the embodied soul continuously passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. A sober person is not bewildered by such a change.” (Lord Krishna, Bhagavad-Gita 2.13)
So what is the soul then?
The science of the soul has been covered on this site in many ways. Please go to the ‘Science’ section and read ‘The Science of the Soul’.
The soul is basically a minute part of the superior energy of Lord Krishna. Matter is His inferior energy. Every soul is a spark of Lord Krishna, a part of Him. This does not mean we are all God, we have the same qualities as Him, but in minute quantity. Just like a drop of ocean water has the same qualities as the ocean, but the drop can never be called the ocean.
“He expands Himself into many living entities, which are manifested as different species of life..” (Shrimad-Bhagavatam 3.5.6)
A soul (the living entity) can reside in one of 8.4 million species or bodies. A soul within a material body is called a living being.
So when were the souls manifested?
Basically when did the expansion of Lord Krishna into many living entities take place? This cannot be computed. This happened zillions to the power of zillions……. years ago.
Even though Lord Krishna expanded into zillions of souls, He still remains the same. This is the reason why He is called God, the greatest. We cannot be present in two places at the same time, but Lord Krishna is already present in zillions of places within each of the billions of universes at the same time. Each and every place where He is present, He is complete with full functionality. So for example, if all the billions of universes are completed destroyed. If one atom is left. Lord Krishna will expand from that one atom and re-create the billions of universes and enter into each and every atom in every universe. This is how great Lord Krishna is. Another example, if one corona virus is inhaled, it will expand or multiply into millions of corona viruses within hours. From one seed, millions of trees can be created over a period of time. In a similar way, Lord Krishna can expand into zillions of forms instantly.