"He was a true artist and a true New Zealander and a true man.
"Ath was big and bold and exuberant -- he was larger than life, but there was always something humble and vulnerable about Ath ... and above all, he was lovable."
His buildings were his legacy, Neill said.
"Ath's beautiful work lives on with us and so, I think, somehow so does Ath."
Fellow architect and friend Roger Walker said Sir Ian's work would in the future be regarded as having the same influence on Wellington as Frank Lloyd Wright's work had on Chicago.
Sir Ian was appointed as a knight in this year's New Year's Honours list.
Former Environment Court judge Shonagh Kenderdine said Sir Ian would go into battle for his beliefs, "in a way a general would set out on a battlefield".
"But I think it's his compassion, humour and leadership ... those wonderful qualities that I take away from him being knighted."
Former MP Stephen Franks -- Sir Ian's neighbour -- said the architect could move seamlessly from telling a bawdy joke to "extreme earnestness".
"He didn't mind tweaking the nose at convention. He left us much too soon."
Wellington Mayor Celia Wade-Brown said Sir Ian "brought honour to this city he adopted and which had adopted him".
"He changed the face and function of much of Wellington and he also contributed much inspiration to other places."
Sir Ian was a former president of the Institute of Architects and a recipient of the institute's gold medal for career achievement.
An artwork created by Sir Ian was installed in Civic Square, outside of the gallery, before today's commemoration.
Other significant Wellington buildings designed by Sir Ian and his practice included the First Church of Christ Scientist, Telecom House, Massey University Te Ara Hiko College of Creative Arts, the new Dowse Art Gallery, and his own house, which he built over the course of four decades.
