The town was officially renamed Kingstown in 1821 in honour of a visit by the British King George IV, but reverted to its ancient Irish name by resolution of the town council in 1921. This monument was erected to mark the occasion of the visit.
The inscription is as follows:
To Commemorate the visit of the King to this part of his
dominions and to record that on the 3rd of September 1821
His Majesty in person graciously named this Asylum Harbour
the Royal of Harbour of George IV and on the same day
embarked from hence.
King George arrived in Ireland on his 59th birthday in August 1821 and it was expected that he would arrive in Dun Laoghaire. I think that it was spelled 'DunLeary' at the time. But for some reason [related to too much alcohol] he first landed in Ireland at the West pier in Howth where his footprints were recorded for posterity.
After spending a few weeks having a great time in Ireland the king decided to exit via Dun Laoghaire which was later renamed Kingstown in his honour. The name did not change back until 1922 when Ireland was independent.
The George IV monument was erected about 1823 to commemorate the 1821 visit. However, the monument was controversial from the start. It was lampooned by Thackeray the poet. Also, it was a target for many protesters and attacks including a bombing in 1970, after which one of the 4 balls forming the base was badly damaged and had to be replaced [if my memory serves me well the ball was initially replaced by a block of wood which remained for an expended period].