Umami was proposed as a fifth basic taste by Kikunae Ikeda in 1908, who isolated glutamate as the compound responsible for the savory quality of kombu dashi.
Umami compounds: glutamate (free amino acid), inosinate (from meat/fish), guanylate (from dried mushrooms). The last two synergize strongly with glutamate — combining them multiplies the perceived intensity far beyond additive.
This is why dashi (glutamate from kombu + inosinate from katsuobushi) is so effective. It's also why parmesan on tomato sauce works: both are high in glutamate, and the combination is 8× more intense than either alone.