What is the name of the underwater mountain range that runs through the Atlantic Ocean?

The underwater mountain range running through the Atlantic Ocean is the Mid-Atlantic Ridge.

The Mid-Atlantic Ridge is a mid-ocean ridge and divergent plate boundary that stretches from the Arctic region into the South Atlantic. Magma rises along its central rift, cools, and forms new oceanic crust as tectonic plates slowly move apart. Its average spreading rate is about 2.5 centimeters per year.

In the North Atlantic, the ridge separates the North American Plate from the Eurasian and African plates. In the South Atlantic, it separates the South American and African plates. Although most of it lies underwater, the ridge reaches the surface in places, most famously in Iceland.

The ridge became central to the acceptance of seafloor spreading and plate tectonics. Sonar mapping and research by scientists including Marie Tharp and Bruce Heezen revealed its continuous rift valley and helped show that the ocean floor is geologically active.