Marya is a gypsy woman whom raised Pietro Maximoff (Quicksilver) and Wanda Maximoff (Scarlet Witch). After their children Ana and Mateo died, she and her husband Django's were devastated with their loss, and the couple moved on by traveling. It was then that the High Evolutionary brought the devastated couple two abandoned children whom they raised as their own.
Marya Maximoff was created by David Michelinie and John Byrne and first appeared in The Avengers Vol. issue 182 (1979). She was always portrayed as being the adoptive mother of Quicksilver and the Scarlet Witch.
However, more recently it was hinted in Uncanny Avengers Volume 2 that Magneto and Magda Lehnsherr where not truly the twins' parents. It was hinted by the High Evolutionary that Marya and Django Maximoff where Pietro's and Wanda's true parents all along.
Major Story Arcs
However after the revelation that Magneto was never the twin's father it's revealed by High Evolutionary that Django Maximoff was Pietro's and Wanda's true father all along.
X-Men Days of Future Past (2014)
Actress Zehra Leverman plays Ms. Maximoff in the X-Men movie. She is seen as the mother of Quicksilver and a little girl whom is most likely the Scarlet Witch (unofficially, since the movie-rights to Scarlet Witch belong to the Marvel Studios).
X-Men Apocalypse (2016)
Actress Zehra Leverman reprises her role as Marya Maximoff in the newest X-Men movie.