Old salt Papudo is likely the brother of Dickie Duck's father, and, presumably, a relative of Moby Duck. Like Moby, Papudo is an old salt who likes to tell tall tales of his seafaring days to his niece, and he often hangs out with her and her friends.
Behind the scenes
Papudo Duck first appeared in the 1986 promotional illustration There they are! Dickie's friends!. He was meant to become a recurring character in the Brazilian comic series A Turma a Pata ("Dickie's Class Friends"), centering on Dickie Duck and her close teenage friends. For unknown reasons, he was scrapped, and only appears to this day in this illustration.
His surname of Duck was not given in the illustration or any known official material; rather, Duck being his surname is simply an assumption based on the fact that he is explicitly stated to be the uncle of Dickie Duck and doesn't bear much resemblance to Dickie's grandmother, Goldie O'Gilt, whose son he would be if he was Dickie's maternal uncle, thus leading to the conclusion that he is Dickie's paternal uncle and bears the same last name as her, Duck. However, it is still a possibility that he is an uncle by marriage or, perhaps, some other distant relative referred to as "uncle". It is just easiest to presume that his relation to Dickie is less complicated and that he is her paternal, biological uncle.