What is the name of the scientist who discovered the electron?

The question probably refers to 'the modern theory of electron clouds'. This theory is now almost a century old and is called quantum mechanics. It describes the states of electrons in an atom as 'electron clouds', so-called orbitals, which indicate the probability distribution of the electron wave function. In contrast to a naive classical picture that pictures electrons as point-like particles with given velocity and position, the quantum mechanical picture describes electrons as smeared-out matter waves following the Heisenberg uncertainty principle.