The Royal Institute of British Architects (RIBA) is a professional body for architects primarily in the United Kingdom, but also internationally, founded for the advancement of architecture under its charter granted in 1837 and Supplemental Charter granted in 1971. 

Originally named the Institute of British Architects in London, it was formed in 1834 by several prominent architects, including Philip Hardwick, Thomas Allom, William Donthorne, Thomas Leverton Donaldson, William Adams Nicholson, John Buonarotti Papworth, and Thomas de Grey, 2nd Earl de Grey. 

After the grant of the royal charter it had become known as the Royal Institute of British Architects in London, eventually dropping the reference to London in 1892. In 1934, it moved to its current headquarters on Portland Place, with the building being opened by King George V and Queen Mary. 

It was granted its Royal Charter in 1837 under King William IV. Supplemental Charters of 1887, 1909 and 1925 were replaced by a single Charter in 1971, and there have been minor amendments since then.
Who was present for its opening?
 with the building being opened by King George V and Queen Mary