What alien species is Spock's mother?

Spock's mother is human. Her name is Amanda Grayson, a human woman from Earth who married the Vulcan ambassador Sarek and became the mother of Spock.

Amanda's background helps explain Spock's unusual identity. Spock was born with both human and Vulcan heritage, and he was raised on Vulcan while exposed to human values through his mother. He often struggled between Vulcan ideals of logic and the emotions associated with his human side. That internal conflict became one of the defining themes of his character.

Amanda first appeared in the episode “Journey to Babel,” played by Jane Wyatt. The episode introduced her as a warm, perceptive figure who could understand both her husband and her son. She was not a Romulan, Klingon, or Vulcan: Sarek was Vulcan, while Amanda was human. Spock is therefore half human and half Vulcan, even though he spent much of his childhood in Vulcan society.

Amanda's character also appears in later Star Trek productions and alternate-timeline stories. In the 2009 film Star Trek, she was played by Winona Ryder. Her human heritage is essential to understanding why Spock's identity and emotional life differ from those of most Vulcans.