What was the first religion ever created?

This is a very interesting question, and one that scholars have struggled with and pondered about since the dawn of the study of religion. So you are definitely in good company! Your question stems from the definition of religion itself, which is also a point of contention among scholars of religion. The definition of religion tends to differ depending on what academic discipline is used as a lens with which to view the world. For example, a sociologist and a psychologist will have differing definitions of religion, since their academic fields focus on differing aspects of the human experience. These discipline-specific definitions function well enough for the scholars who employ them, but they are far from comprehensive. In the academic study of religion, which itself is a composite field, definitions of religion tend to be more inclusive. The question of the first religion, therefore, will depend on how you choose to define religion. My following response is general, and should apply to most disciplines.

Before organized religion, there was religiosity. This refers to archaeological hints, such as personal items included in graves, strange markings and drawings, and figurines, that suggest the group of people being studied had some conception of a ultimate power or life after death. We do not know the extent of these beliefs because the evidence of religiosity is purely archaeological. These hints may be indicative of the first religions.

Since we do not know the details of this early religiosity, most scholars do not consider this the first religion, as religion usually is considered to be more solid and organized. The next candidate would be the belief systems of hunter-gatherer groups. We know more about these early religions because some of these groups are still extant today. In general, they revered the moon, as well as a totem animal, and a life-force that inundated all living things. This life force, in a certain South-Pacific group, was known as manna, which is now a general term. The religious leader of these groups was known generally as a shaman. The shaman was the connection between the physical world and the spiritual world, and was able to cross over via symbolic death to relay information. These early religions can be considered the first.

However, if the question is referring to which of the large, modern, organized religions originated first, then the answer is different. In this case, the general answer would be "Hinduism", even though the conception of Hinduism as a singular religion is modern. More accurately, Vedism, the precursor to Hinduism, Buddhism, and Jainism, is oldest. This religion is reflected in the Vedas, a group of oral compositions used for an elaborate ritual sacrifice.

So, once again, the answer depends on your definition of religion. Good luck!