Why there is black god/kali in Hinduism?

Why there is black god/kali in Hinduism?

A detailed, two-page proposal, the proposal must contain a proposed thesis and a bibliography. The paper must be at least 10 pages in length NOT counting the bibliography, but may include the foot or endnotes. The paper will be formatted according to this style. It should be written in Times New Roman 12pt font and double spaced. A maximum of two online sources may be used, but most of your information must come from conventional books or research paper. The paper must be written using the Chicago Manual of Style method.