Gru's mom* is a gruff and abrasive woman...tough as nails and old-world in her mannerisms and style.  She raised Gru pretty much on her own.  But don't be fooled...nurturing was neither her strong suit nor her preference.  Every time young Gru would attempt to gain his mother's approval or affirmation, she would shoot him down with some snide or disdainful remark.  She's not a very nice lady, or a very good mother, except when she's comparing others to herself.  But she loves Margo, Edith and Agnes very much, and that's something in her favor.

(* On the imdb.com page for Dispicable Me, in the trivia section, it says "in the Gru family tree, you can see Gru's mother's name is Marlina, and his father's name is Robert."  Of course, other than seeing Robert and other ancestors in Gru's family tree, we never actually get to see any members of his family, during the movie, except his mother.)

Gru and his mother clearly are not native to the United States (where they live), and their broken English accent would seem to indicate that they originated from somewhere in central to southeastern Europe.

Of course, she's also an accomplished martial artist...