It was built by the Moghul Emperor, Shah Jahan, in memory of his wife Mumtaz Mahal,designed by Ustad Isa of Iran, completed in 22 years (1631 to 1653) by 20,000 artisans brought to India from all over the world.
Now listen to the alternate story(theory?)
Taj Mahal is not Queen Mumtaz Mahal's tomb, but an ancient Hindu temple palace of Lord Shiva (then known as Tejo Mahalaya), worshipped by the Rajputs of Agra city.
This theory was proposed by Professor P.N. Oak. He has put forward evidences to support his theory.
P. N. Oak (born 1917), full name Purushottam Nagesh Oak, is a Maharashtrian Brahmin historian associated with the Hindutva movement. Because of his association with the Hindutva movement, many consider his theory as manifestations of anti-Muslim sentiment.
In the course of his research, Oak discovered that the Shiva temple palace had been usurped by Shah Jahan from then Maharaja of Jaipur, Jai Singh. Shah Jahan then remodelled the palace into his wife's memorial.
In his own court chronicle, Badshahnama, Shah Jahan apparently admits that an exceptionally beautiful grand mansion in Agra was taken from Jai Singh for Mumtaz's burial. The ex-Maharaja of Jaipur is said to retain in his secret collection two orders from Shah Jahan for the surrender of the Taj building.The use of captured temples and mansions as a burial place for dead courtiers and royalty was a common practice among Muslim rulers. For example, Hamayun, Akbar, Etmud-ud-Daula and Safdarjung are all buried in such mansions.
Here is a copy of a page of the Badshahnama This is from the Government of India's National Archives, and available from the instituional libraries dealing with the medieval history of India.
Had Shahjahan really built the Taj Mahal as a wonder mausoleum, history would have recorded a specific date on which she was ceremoniously buried in the Taj Mahal. No such date is ever mentioned. This important missing detail decisively exposes the falsity of the Tajmahal legend.
Even the year of Mumtaz's death is unknown. It is variously speculated to be 1629, 1630, 1631 or 1632. Had she deserved a fabulous burial, as is claimed, the date of her death had not been a matter of much speculation. In an harem teeming with 5000 women it was difficult to keep track of dates of death. Apparently the date of Mumtaz's death was so insignificant an event, as not to merit any special notice. Who would then build a Taj for her burial?The usual explanation that the term Taj Mahal derives from Mumtaz Mahal is illogical in at least two respects. Firstly, her name was never Mumtaz Mahal but Mumtaz-ul-Zamani,' he writes. 'Secondly, one cannot omit the first three letters from a woman's name to derive the remainder as the name for the building.
Oak also points out a number of design and architectural inconsistencies that support the belief that the Taj Mahal is a typical Hindu temple rather than a mausoleum.Many rooms in the Taj Mahal have remained sealed since Shah Jahan's time, and are still inaccessible to the public. Oak asserts they contain a headless statue of Shiva and other objects commonly used for worship rituals in Hindu temples.
Fearing political backlash, Indira Gandhi's government tried to have Oak's book withdrawn from the bookstores, and threatened the Indian publisher of the first edition with dire consequences.
The only way to really validate or discredit Oak's research is to open the sealed rooms of the Taj Mahal, and allow international experts to investigate.
On July 14 2000 the Supreme Court in New Delhi dismissed a petition that sought to force a declaration that a Hindu king built Taj Mahal, as P.N. Oak has claimed. The court reprimanded the petitionersaying he had a "bee in his bonnet" about the Taj.
In 2005 a similar petition was dismissed by the Allahabad High Court. This case was brought by Amar Nath Mishra, a social worker and preacher who says that the Taj Mahal was built by the Hindu King Parmar Dev in 1196.