In Star Trek (2009), the Romulan commander seeking revenge on Spock is Nero.
Nero is a mining-ship captain from the future who blames Spock for the destruction of Romulus. After traveling backward through a black hole, he attacks the USS Kelvin, creating the alternate timeline used by the film. His ship, the Narada, is vastly more powerful than the Federation vessels encountered in the 23rd century.
Australian actor Eric Bana portrayed Nero. Unlike many earlier Star Trek antagonists, Nero is not pursuing territorial conquest or a military objective alone; his actions are driven primarily by grief and personal vengeance. His conflict with Spock connects the new film to the original continuity while allowing a separate timeline.
Khan is the villain of The Wrath of Khan and Into Darkness, while Krall appears in Star Trek Beyond. Those names are therefore frequent but incorrect alternatives for this question.