Momma Robotnik is the mother of Doctor Robotnik, and if you thought he was evil, she's twice as worse!
In her first ever appearance, Momma Robotnik escaped the Mobius Home for Really Bizarre Mothers, enraged that her son has forgotten it's her birthday. Initially she wanted him to cut down the Mobian Natural Park (the trees spoiled the view from her bedroom window), but after witnessing defeat at the hands of Sonic the Hedgehog, she wanted to see him crushed.
Later on, she escaped the Home again. Disowning her 'failure of a Son' and stealing his fortress, Momma organized and succeeded in the adoption of Sonic. Her plot was eventually uncovered, and the adoption was deemed null.
Momma would continue to make several more unexpected visits throughout the series to assist her son in defeating Sonic, but failed every time.
Archie Sonic Continuity
At an unknown point in time during the past few decades of Mobian history, "Momma" Robotnik (first name yet to be revealed) was imprisoned in the Mobius Home for Really Bizarre Mothers. It was only when she discovered that her son had dwelled into insanity (see STH#200 "Turnabout is Fair Play") that Momma finally escaped and rushed straight to the Eggdome to (quite possibly) whack some sense back into him. Her plans are yet to be revealed.
It's possible that Momma Robotnik is Snively's Grandmother.
Momma Robotnik has black eyes with red/black pupils and blue/red irises, a pink nose, wears a bulging pink dress with a large green hat and black shoes.
On the first episode she appeared in (Momma Robotnik's Birthday), she sported a mustache just like her son. From Momma Robotnik Returns onwards, the 'stache was dropped.
-Momma Robotnik has a laugh like a donkey.
-She is also (with the exception of the Boogey-Man) the only character Doctor Robotnik seems completely afraid of.
-The spelling of her name is often something of a debate in the fandom. The episode titles confirm her as 'Momma' while some fans argue it should be 'Mama'. In conclusion, it all comes down to author intent in which it should be, though the canon spelling IS 'Momma'.
-Writer Paul Agnew has stated that Momma Robotnik is his favourite female Sonic character of all-time. However, some argue this could be a false lead (he is known to drop fake hints from time to time) on revealing a true favourite.