Gerald Samson

Gerald Samson (better known as "Baby Gerald" or "The Monobrow (or Unibrow) Baby") is Maggie's arch-nemesis. He has a unibrow (hence his nickname).

Biography
Lisa has referred to Baby Gerald as Maggie’s rival. Gerald is distinguished by his unibrow, being one of the few characters in the show to have one.

On a few occasions, Gerald has been shown being pushed in a stroller by his mother outside the Simpsons’ house, with the two babies glaring at each other, the camera focusing on their narrowed stares. Homer often mistakes Maggie for Baby Gerald.

Gerald apparently has a history of causing large scale public incidents and was once rescued from an unspecified disaster by Bart’s mail order “wonder dog” Laddie. Both dog and baby were participants in a ceremony presided over by Mayor Quimby, during which the mayor inquired, "Baby Gerald, we can't help but wonder what mischief you'll get into next".

Future
It is revealed that Maggie and Baby Gerald stopped being enemies, got married, and even had a baby together. The baby was named Margaret "Maggie", Jr. after her mother.

Trivia

 * In the new Simpsons sequence, when Marge goes to the super market, it shows Maggie shaking her fist at Baby Gerald.
 * Baby Gerald's last name was seen in a label of the Simpsons.
 * He is voiced by Hank Azaria (Despite not even talking).