Algol is a three star system containing an eclipsing binary pair. According to Burnham Algol is one of the most famous variable stars in the sky.
The primary, Algol A, is a blue B8V main sequence star. This spectral type implies that an effective temperature of 12000 K, a diameter 3 times that of the sun, and a luminosity about 170 times that of the sun and a mass of about 5 times that of the sun.
The secondary, Algol B, is a yellow G8IV subgiant that passes in front of Algol A every 2.86739 days producing a decrease in brightness of about 1.3 magnitudes. The entire eclipse lasts about 10 hours. Burnham estimates the distance between A and B at about 6 million miles. So the separation between the stars would be comparable to the their combined diameters.
The data given by Burnham for Algol B imply a luminosity about 1.5 times that of the sun. Algol B produces eclipses of the A component, because it is much less luminous than that star. The diameter of B would be about 3 million miles, making it in fact slightly larger than A in diameter.
Algol C was first detected by its effects on the orbit of the AB pair. C orbits with a period of 1.86 years. Burnham puts the radius of the orbit at about 0.5 AU. The spectral type of C is uncertain. It is however, certainly brighter than the sun and at least as massive.