J.S. Bach, who apparantly liked to be referred to as Sebastian, was the
culmination of the
baroque period. In fact, he is sometimes referred to as
High Baroque.
In his lifetime he had many, many children including Wilhelm Friedemann, and Carl Phillipe Emmanual. His wife was Anna Magdalena, for whom the Anna Magdalena Notebook was compiled.
Sebastian was not known in his lifetime as the great composer he is today. In fact, he was only the second greatest organist of his day. The greatest was considered to be Telemann. Sic transit gloria.
The style of composition of Bach and his contemporaries is known as polyphonic. In this style there is no accompaniment as we understand it in, say Beethoven, or Chopin. It can be thought of more like the interweaving of voices in a choir. After all, there were choirs long before there were pianos.
For pianists Bach is so often one of the hardest to perform for just this reason. The left hand is not an accompaniment to the right hand. In fact, it has an independant melody all in its own right, such as in the Inventions.
Even more, in the Sinfonia, also known as the Three Part Inventions, and especially the fugues in the Well-Tempered Clavier, each may perform several independant voices, and exchange them back and forth.
One of the most eccentric, yet well-respected performers of polyphonic work, including Bach, was Glenn Gould, a graduate of the Royal Conservatory of Music of Toronto. His recording of the Goldberg Variations for Columbia Masterworks in the late 50's--the first recording, not the second one done near the end of his life--is considered an absolute gem of clarity, precision, and passion.