Sri Ramakrishna Paramhansa (February 18, 1836 - August 16, 1886) was an Bengali religious leader. While a worshipper of Kali, he preached that all religions lead to the same goal, and taught spiritual religion against ritualism. The Hindu renaissance that India experienced in the 19th century can be said to have really begun with his life and work.
Although the Brahmo Samaj and the Arya Samaj preceded the Ramakrishna Mission, their influence was limited. With the emergence of the Mission, however, the situation changed dramatically. The Ramakrishna Mission was founded by Swami Vivekananda, but it was his spiritual master, Ramakrishna, who indirectly provided the main impetus for this movement. The life and teachings of this man of God have had a tremendous impact on the world at large as well as on the people of India.
His experience of nirvikalpa samadhi (absorption in the all-encompassing Consciousness) gave Ramakrishna an understanding of the two sides of maya (illusion), to which he referred as avidyamaya and vidyamaya. He explained that avidyamaya represents the dark forces of creation (eg sensual desire, evil passions, greed, lust and cruelty), which sustain the world system on lower planes of consciousness. These forces are responsible for human entrapment in the round of birth and death, and they must be fought and vanquished.
Vidyamaya, on the other hand, represents the higher forces of creation (e.g. spiritual virtues, enlightening qualities, kindness, purity, love, and devotion), which elevate human beings to the higher planes of consciousness. With the help of vidyamaya, devotees can rid themselves of avidyamaya and achieve the ultimate goal of becoming mayatita - that is, free from maya.
This experience of nirvikalpa samadhi also convinced Ramakrishna that the Gods of the various religions are merely so many interpretations of the Absolute, and that the Ultimate Reality could never be expressed in human terms. This confirmed the Rigvedic proclamation that "Truth is one but sages call it by many a name". As a result of this insight, Ramakrishna actually practised Islam, Christianity and various sects within Hinduism at different times.
The four key concepts in Ramakrishna's teachings were the following:
the oneness of existence
the divinity of human beings
the unity of God
the harmony of religions
It could be argued that Ramakrishna's vision of Hinduism, and its popularisation by western converts like Christopher Isherwood, have largely coloured western notions of what Hinduism is.