As the volcano erupted it deposited 6 meters of ash on parts of Malaysia and a 15 centimetres thick ash layer over the entire Indian subcontinent, and acid rain fell for years. The temperature of the planet fell abruptly 3–5°C and according to some (based on ice cores for Greenland) it jump -started the next global ice age.
It just so happens that this massive environmental catastrophe coincides with evidence for a massive human population decline resulting in a genetic bottleneck. According to the Toba catastrophe theory the resulting 6 to 10 year volcanic winter destroyed most of the vegetation in the area where humans would have been living and may have reduced the population to as few a 1000 breeding pairs.
There is some good evidence for this genetic bottleneck, and many geneticists feel that evidence suggests that all living humans, despite apparent variety, descend from a very small population, perhaps between 1,000 to 10,000 breeding pairs dating to about 70,000 years ago. It is also known that Eastern African chimpanzee, Bornean orangutan, central Indian macaque, and tigers, all recovered from population bottelnecks dating to around the same time. All of which would seem to fit neatly with the Toba super volcano event and the Toba catastrophe theory.
But as it always is in science nothing is neat or easy, and contradictory evidence is just as strong.
Today, what's left of the volcano is a huge, beautiful, water-filled crater called Lake Toba. But it's still a volcano, and may yet erupt again. Read more about it at Atlas Obscura. Link