The scientist who formulated the principle that the position and speed of an electron (or any other quantum particle) are uncertain is Werner Heisenberg.

This principle is known as Heisenberg's Uncertainty Principle. It states that it is impossible to simultaneously know both the position and momentum (which is related to speed) of a particle with absolute certainty.

The more precisely you know the position of a particle, the less precisely you can know its momentum, and vice versa. This principle is a fundamental concept in quantum mechanics.