John Nash (1752-1835) seems to have been a brilliant but somewhat slapdash and erratic man. Born the son of a poor Lambeth millwright, he apprenticed with Sir Robert Taylor to train as an architect, but got bored quickly, broke away from Taylor and formed his own practice. His first big project was a terrace of London houses faced with stucco, to look like stone, but nobody wanted the houses and the project fell flat. Nash landed on his feet however: shortly after this he was bequeathed a large sum of money, and retired to Wales to live a life of leisure. Two years later he had lost the lot in ill-judged speculations and bad investments, and had to return to architecture in London. Here again he had good luck, coming to the attention of the Prince Regent (later George IV) who befriended him and commissioned him to build a new park and terraces to create a grand aspect for the royal residence, Carlton House.

There are various theories about how Nash and 'Prinny' became friends, including speculation that Nash's much younger wife was one of the Prince's many mistresses - of course the Prince may just have been very interested in architecture, as demonstrated by the Brighton Pavilion, which Nash would remodel in grand Oriental style later on. He was definitely very keen on Nash's designs for the Park, which radically re-landscaped a large chunk of Central London and would provide pleasure gardens and open parkland bounded by broad, sweeping streets filled with houses of great beauty and intricate design, creating a triumphal processional way through North London down to Carlton House.

It was a fitting time for a grand building project: Wellington had recently trounced the French, and the Empire was safe for the time being. Yet, at the same time, the industrial revolution was hitting the poor harder than ever before. The new rich who would buy Crown leases on Nash's houses around the park were far removed from the squalid slums just a few streets away from Portland Place and the grand circuses on Piccadilly, Oxford Street (then the Oxford Road) and inside the park itself. Not everyone was keen on the style, either. Maria Edgeworth, the novelist, said at the time that she was: "properly surprised by the new town that has been built in Regent's Park – and indignant at the plaister statues and horrid, useless domes and pediments crowded with mock sculpture figures which damp and smoke must destroy in a season or two".

For all his creative genius, Nash's building techniques left much to be desired. They were bold and imaginative, but the damp and slapdash stucco-and-deal construction meant that structurally they were very unsound, which has made for a good deal of maintenance and restoration work on the surviving houses. (Nash's later work on Buckingham Palace was so badly mismanaged that his was dismissed from the project halfway through!) The Theatre Royal in the Haymarket is one of his better surviving buildings from the grand Regent's project, which was never completed as they ran out of money in 1825, just as work on Regent Street was about to go ahead. The Duke of York's Steps were built instead.

Here's a list of Nash terraces that were completed:

Hanover Terrace, 1822
Sussex Place, 1822
Cornwall Terrace, 1821
York Terrace, 1822
Ulster Place, 1824
Park Crescent, 1819-21
St. Andrew's Place, 1823-26
Chester Terrace, 1825
Chester Place, 1825-26
Cumberland Terrace, 1826
Gloucester Gate, 1827
Kent Terrace, 1827
Clarence Terrace, 1823
York Gate, 1822
St Marylebone Parish Church, 1817
Park Square West, East, 1823,1824
Albany Terrace, 1820-23
Cambridge Terrace, 1825
Christ Church, 1837
Cumberland Place, 1826
St Katherine's Church, 1826

And here's a time-frame for Regent's Park:

1539 Marylebone Park acquired by King Henry VIII. Mainly forested and used as a Royal hunting ground.
1651 Sold by Cromwell during the Commonwealth to raise finances. New owners felled most of the trees to sell the timber.
1660 Restoration of the Monarchy. Park returned to the Crown.
1668 Land declared disparked. Mainly let for dairy farming for the next 100 years.
1760 King George III agreed to give all the revenues from Crown Lands to parliament in exchange for the Civil List.
1793 John Fordyce appointed as the Crown surveyor-General
1794 Fordyce commissioned a major survey of the park.
1806 John Nash and James Morgan appointed as architects to the Department of Woods and Forests.
1810 Commissioners of Woods and Forests instructed Nash to develop a plan for the park.
1812 Work started on the new Regent's Park.
1820-28 Most of the terraces and villas were built during this period.
1826-28 The Zoological Gardens were developed and opened.
1835 Part of the park opened to the public for the first time.
1932 The first open air theatre production (Twelfth Night).
1939-45 Second World War. Severe damage caused to most of the villas and terraces.
1946 The Gorell Committee appointed to advise on the future of the terraces.
1947 The Gorell Committee recommended that the terraces should be saved.
1956 The Commissioners of Crown Lands were re-organised as the Crown Estate Commissioners.
1957 The Crown Estate Commissioner's issued a statement confirming that the Nash terraces would be preserved.
1957-99 All the terraces and villas within the Park have been restored during this period.