The family name at the time was Wesley, not Wellesley. Arthur's eldest brother (there were two elder — Richard, William (later Wellesley-Pole) and and an elder sister, Anne, followed by Henry and Gerald Valerian. The grand father was Richard Colley (or Cowley or Cooley — which would be most applicable in eighteenth-century Ireland? Despite this the family preferred the Anglicized version Colley). The name Wellesley was adopted by Richard (Arthur's eldest brother) when in search of Marquessate. Afetr service as Governor General of India, he became Marquis Wellesley ignoring the Mornington, because he thought it reflected a genealogy back to Norman, which the Cooleys didn't have.
Recommended reading
James, L. The Iron Duke: a military biography of Wellington. London, 1992.
Longford, E. The Years of the Sword. London, 1969.
The late Lady Longford (who married Frank, later Lord, Longford and had access to family archives and those of HM the Queen and the Dutch royal family - Kitty Wellington, wife of 1st Duke, m 1807, was a daughter of Lord Longford) can be regarded as the definitive author on the subject.
Longford, E. Wellington: Pillar of State. London, 1972.
Last modified 19 March 2008