The 'plum pudding' model of the atom was proposed by JJ Thomson, who had also discovered the electron. It was put forth before the discovery of the nucleus.

In 1899, Thomson published a description of his version of the atom, commonly known as the "plum pudding model." An excerpt of this paper is found on the Chem Team site.

An atom is made of tiny negatively charged electrons dotted about a positively charged sphere like a plum pudding. 1909-1911 Rutherford (and Geiger and Marsden) ...

Everyone at that time imagined the atom as a "plum pudding." That is, it was roughly the same consistency throughout, with negatively-charged electrons scattered about in it like raisins in a pudding.

The atom has fascinated scientists for thousands of years and is the building brick which makes up all matter. But have you heard of the ‘plum pudding’ model when it comes to the atom ...