From the Super Mario Wiki, the Mario encyclopedia
Bowser's mother is the mother of Bowser. She primarily appears in The Super Mario Bros. Super Show! episode "Do You Princess Toadstool Take This Koopa...?". She is portrayed as being loudmouthed and overbearing, appearing to be somewhat disappointed in and continuously doting on her son, and is also hinted at being somewhat of a glutton. Her son constantly refers to her as "Mama", while she calls her son, "Koopums".
King Koopa first mentions her in the episode while making preparations for the wedding with Princess Toadstool, who he had blackmailed into marrying him. Unable to think of any friends to invite, King Koopa tells Mouser to invite his mother, saying she will come for the cake.
King Koopa's mother arrives at the castle as he is instructing his Koopa Troopa band to play better. Immediately praising her son for finally finding a wife to settle down with, Koopa's mother, upon seeing Princess Toadstool, proclaims that after they are married, they would honeymoon with her in "the foulest, smelliest swamp in seven worlds." Toadstool sobs after hearing this, which King Koopa's mother misinterprets as her being overcome with joy.
As the wedding is about to begin, Koopa's mother scolds her son for not being dressed properly, King Koopa hurrying off to get ready. As Koopa put on his wedding jacket and pants, his mother calls for her son to hurry. Koopa impatiently returns to the wedding with Mouser, not noticing that he had left behind his magic wand, which Mario manages to claim. Before Princess Toadstool can say "I do", Super Mario, Super Luigi and Toad appear to interrupt the wedding with a hail of fireballs. After Princess Toadstool calls the wedding off upon learning that King Koopa had double-crossed her, his mother voices her outrage that she now has to tell all their relatives that her son is still a bachelor. She then punishes him by ordering him to sit in the corner for six days, as Koopa falls on his face.