In Biggles and the Leopards of Zinn, Otto Ducard was a European adventurer in Africa who, with his partner, Akmet Batoun, prospected illegally for diamonds in the Zinda region in Uganda. In the process, they interfered with and terrorized a tribe of Zinns into providing forced labour, an event which prompted the British authorities to send Biggles to investigate.
Ducard was born in Cape Town of a Dutch father and English mother. When young, he went to jail for illegal diamond buying. Thereafter he wandered all over Africa. It was while sheltering from the police in the international zone of Tangier that he met his partner Akmet Batoun. The two then went to the Belgian Congo where they attracted the attention of the Belgian authorities for causing trouble among the natives in Leopoldville.
Some time before the events in the book, Ducard had met a dying man in Nigeria who told him there was a fortune to be had at Lake Jumu. Thinking that the man meant diamonds, Ducard and Batoun planned to mount an expedition. They had some difficulty finding porters at first but Batoun called on the services of N'Bulu, an African witch doctor, who managed to recruit a party of his leopard men.
Arriving at Lake Jumu, the party used a mixture of superstition and force to force the Zinn tribe to work for them, digging holes in the ground to prospect for diamonds. At the same time, the Zinns were bribed by being fed with large amounts of fish which the party collected by tossing dynamite into the lake.
Ducard gradually became disillusioned with Batoun's methods, especially with the intimidation and violence employed by N'Bulu, which included the murder of two British colonial officers, James and Major Wilson and the Askari Sergeant Abdullah I'Mobo. However he could do little as the real power lay with N'Bulu, who would only take orders from Batoun.
When Ducard first met Biggles, Biggles gave him a firm ultimatum to leave Lake Jumu and return to the Belgian Congo or he would be forced to expel the expedition by force. Although Ducard put up a defiant stance for the benefit of Batoun, he later approached Biggles privately to say that he was pulling out.
The next day, Biggles found that the expedition had indeed abandoned its camp but Ducard had been left mortally wounded nearby. He survived long enough to tell Biggles that there had been a violent argument between him and Batoun about whether to stay or go. There had not been enough food to get back to the coast so Batoun had shot him. Before dying, Ducard warned Biggles that his partner would come back to continue prospecting. He had merely left to gather a larger force to confront Biggles with.
Ducard was described as between fifty and sixty, stocky and broad shouldered, with a bushy, untrimmed beard turning grey hiding the lower part of a weather-beaten face. He looked, according to Johns' words, a strong character, but not, ultimately, as strong as he needed to be to control the expedition he thought he was the leader of.