Sir Joshua Lavish, now deceased, was in charge of the Royal Bank of Ankh-Morpork before Moist von Lipwig. He was married to Topsy Lavish, who was once his mistress. He left her 50% of the Bank in his will with a further 1% going to the dog Mr. Fusspot, thus preventing the rest of the Lavish family from gaining control of the bank.
Not much is know about the man except for his sexual appetite. Topsy Lavish was not his first mistress; in fact he seemed to go through them and various sexual partners at a brisk rate. The Chairman maintained a 'lavish' suite at the Bank to entertain them with all the accoutrements of someone who clearly had a diverse sexual appetite. One of the wardrobes of his bedroom was entirely filled with leather and rubber garments, toys and things, (making him a patron of the shop owned by Mr. Tuttle Scrope who specialized in leather goods other than coats.) Even in his old age, his sexual appetites were extravagant, and he demanded much of his conquests.
On viewing the wardrobe's contents, Adora Belle Dearheart described it as a classic case of the Horseradish Sauce Syndrome - you keep adding horseradish to your beef sandwich, increasing the amount until eventually you don't miss the beef. While Moist and Adora are exploring the bedroom, Mr. Fusspot discovers a new rubber toy 'bone' which becomes his favourite chew toy, even offering it to Angua when he proposes to her. It is clear however that Sir Joshua's pleasures did not come cheap and contributed significantly to beggaring the bank while he went through ten tonnes of gold on Seamstresses apart from what, by her own admission, ended up in Pucci Lavish's jewelry box. Sir Joshua Lavish kept extensive and very informative diaries: what he considered were the unimportant bits, such as Bent's true history and what really happened to the gold, were not encrypted. Like that other famous diarist Sir Samuel Pepys, the bits concerning his sexual peccadilloes were encoded but things relating to the affairs of state and the bank were not.
Sir Joshua had two children by a previous marriage, Cosmo and Pucrezia.
It is unknown who Pratchett had in mind for his portrayal of Joshua Lavish but there are certainly many examples in history and in modern times from whom to draw on - wealthy aristocrats with lavish lifesyles, lavish spending habits and lavish sexual appetites. The Lavish family itself resonate with the Medicis of Florence and the Borgias both powerful and manipulative families during the Renaissance in Italy and Europe. Certainly Sir Joshua's son Cosmo Lavish who tries to emulate Vetinari draws his name from Cosimo Medici and his daughter Pucrezia is a clear take off on Lucrezia Borgia.