Albert Einstein did not study cells. He was a physicist. Anton von Leeuwenhoek developed microscopes and studied cells. Robert Hooke was the first scientists to refer to cells in cork tissues. Robert Brown is credited with discovering the cell nucleus.
The job of a scientist is to study natural phenomena with the aim of understanding and perhaps utilizing these occurrences. The study of earthquakes is seismology, and a scientist who studies them is a seismologist.