Swami Vivekananda (Bengali: [Sami bibekanondo] ( listen); 12 January 1863 - 4 July 1902), born Narendranath Datta (Bengali: [norendronath doto]), was an Indian Hindu monk, a chief disciple of the 19th-century Indian mystic Ramakrishna.  He was a key figure in the introduction of the Indian philosophies of Vedanta and Yoga to the Western world and is credited with raising interfaith awareness, bringing Hinduism to the status of a major world religion during the late 19th century. He was a major force in the revival of Hinduism in India, and contributed to the concept of nationalism in colonial India. Vivekananda founded the Ramakrishna Math and the Ramakrishna Mission.
Spiritual apprenticeship - influence of Brahmo Samaj
In 1880 Narendra joined Keshab Chandra Sen's Nava Vidhan, which was established by Sen after meeting Ramakrishna and reconverting from Christianity to Hinduism. Narendra became a member of a Freemasonry lodge "at some point before 1884" and of the Sadharan Brahmo Samaj in his twenties, a breakaway faction of the Brahmo Samaj led by Keshab Chandra Sen and Debendranath Tagore. From 1881 to 1884 he was also active in Sen's Band of Hope, which tried to discourage youths from smoking and drinking.  It was in this cultic milieu that Narendra became acquainted with Western esotericism. His initial beliefs were shaped by Brahmo concepts, which included belief in a formless God and the deprecation of idolatry, and a "streamlined, rationalized, monotheistic theology strongly coloured by a selective and modernistic reading of the Upanisads and of the Vedanta." Rammohan Roy, the founder of the Brahmo Samaj who was strongly influenced by unitarianism, strived toward an universalistic interpretation of Hinduism. His ideas were "altered [...] considerably" by Debendranath Tagore, who had a romantic approach to the development of these new doctrines, and questioned central Hindu beliefs like reincarnation and karma, and rejected the authority of the Vedas. Tagore also brought this "neo-Hinduism" closer in line with western esotericism, a development which was furthered by Keshubchandra Sen. Sen was influenced by transcendentalism, an American philosophical-religious movement strongly connected with unitarianism, which emphasised personal religious experience over mere reasoning and theology. Sen strived to "an accessible, non-renunciatory, everyman type of spirituality", introducing "lay systems of spiritual practice" which can be regarded as prototypes of the kind of Yoga-exercises which Vivekananda popularised in the west.  The same search for direct intuition and understanding can be seen with Vivekananda. Not satisfied with his knowledge of philosophy, Narendra came to "the question which marked the real beginning of his intellectual quest for God." He asked several prominent Calcutta residents if they had come "face to face with God", but none of their answers satisfied him. At this time, Narendra met Debendranath Tagore (the leader of Brahmo Samaj) and asked if he had seen God. Instead of answering his question, Tagore said "My boy, you have the Yogi's eyes." According to Banhatti, it was Ramakrishna who really answered Narendra's question, by saying "Yes, I see Him as I see you, only in an infinitely intenser sense." Nevertheless, Vivekananda was more influenced by the Brahmo Samaj's and its new ideas, than by Ramakrishna. It was Sen's influence who brought Vivekananda fully into contact with western esotericism, and it was also via Sen that he met Ramakrishna.

Q: What was the influence of Brahmo Samaj on Vivekanada?
A: Vivekananda was more influenced by the Brahmo Samaj's and its new ideas, than by Ramakrishna.

Q: What were Samaj's ideas?
A: the founder of the Brahmo Samaj who was strongly influenced by unitarianism, strived toward an universalistic interpretation of Hinduism.
What else happened during Vivekanada's spiritual apprenticeship?
Not satisfied with his knowledge of philosophy, Narendra came to "the question which marked the real beginning of his intellectual quest for God."
Not satisfied with his knowledge of philosophy, Narendra came to "the question which marked the real beginning of his intellectual quest for God."