Karl Buderus, aide to Prince William was the link that Mayer needed to connect him to the Prince's business ventures. Buderus began his career as a tutor to William's illegitimate son by Dorothea Ritter. He moved up into through the financial operations of the Prince and at 33 was appointed to the prestigious post in the War Chest.
The first sign of tacit cooperation between Buderus and Rothschild was in 1794 when Buderus recommended that Mayer be allowed to join five other financiers in bidding for the sale of some English bills.
Unfortunately,the recommendation was ignored but in 1796 Buderus tipped off Mayer that he should offer some bonds to the War Chest at a lower price than the other two financiers. That relatively small sale gave Mayer a foothold into William's vast holdings. In the years following Mayer steadily increased his share of William's investment business. He was involved in as many as 11 major loans, purchased real estate for the Prince, and continued to supply him with the medals for his precious medal collection.
During the French occupation Buderus made the hazardous trip through French lines to successfully smuggle out bonds held by William.
In addition to the bonds left to Mayer, William himself smuggled out chests of valuables; 24 chests of securities, coupons, silver and clothes were hidden under the staircase in the north wing of his castle, 24 more stuffed with the War Chest papers were concealed in another part of Wilhelmshohe, in the cellar of a nearby building another 24 chests held more papers, porcelain, and clothing, two friends secured another 29 chests. Finally, at his hunting lodge, William hid 47 chests of silverware.
Buderus and Mayer continued their friendship and business partnership throughout their lives.