The electron was discovered by J.J. Thomson in 1897.
He was conducting experiments with a cathode ray tube (a glass tube with very low-pressure gas and electrodes at each end). When an electric current passed through the tube, he observed a stream of particles (called cathode rays) moving from the negative electrode (cathode) to the positive electrode (anode).
Thomson showed that these rays were made of tiny, negatively charged particles much smaller than atoms. He called them corpuscles, which were later named electrons.
This discovery was very important because, before this, atoms were thought to be indivisible. Thomson’s finding proved that atoms have smaller subatomic particles. Later, he also proposed the “plum pudding model” of the atom, where electrons were embedded in a sphere of positive charge.
So, the credit for the discovery of the electron goes to Sir J.J. Thomson.