Because lions only inhabit certain limited parts of Africa, which is a very large continent with varied geology, they cannot accurately be said to dominate wildlife on that continent, though they are apex predators who tend to be at or near the top of their ecosystem's food chain. And while lions are skilled hunters and fierce predators, some other predators, such as hyenas, have been known to outcompete and even dominate lions.
As of 2015, the lion is considered a threatened species. Its habitat, which once extended far north of Africa, possibly as far west as Greece and throughout most of India, has become significantly diminished over time, making them too scarce to be truly dominant. In the areas where the lion still flourishes, it typically exists near the top of the ecosystem's predator chain, though other animals may be able to claim the top spot.
About 10,000 years ago, lions were one of the most dominant large land mammals in Africa. However, even when the lion's habitat was not as diminished as it has become in the 21st century, humans were arguably more dominant than lions, being more widespread and ultimately more capable of survival.