The golden Mausoleum of Ferdinand II and its church are the brainchild of Giovanni Pietro de Pomis.
Muli-talented Italians have a long history of prettifying Graz. A Lombardian by birth, de Pomis was the court artist and favored pet of Ferdinand II. Like Domenico dell’Allio, de Pomis earned his keep as a fortress builder while he indulged his imagination as a domestic architect.
He was part of the team that created Schloss Eggenberg – you can view his portrait of Archduke Ferdinand as Fighter for a Righteous Cause in the Alte Galerie – and went solo to paint the original facade of the Gemaltes Haus and design the Mariahilferkirche (where he is buried).
In-between these projects, de Pomis found time to have 13 children, create the Confraternity of Painters in Graz, and lobby to become a noble.
He also, apparently, dipped his hand into the Imperial kitty.* As Wikipedia politely notes, his later reputation was marred “misappropriation of construction funds.” (Some things never change.)
De Pomis died at the age of 63 without ever seeing his Mausoleum completed. Fischer von Erlach finished the task many years later.
* See p. 13 in Ferdinand II, Counter-Reformation Emperor, 1578–1637 by Robert Bireley.