Margo Gru is one of Felonius Gru and Lucy Wilde's adopted daughters and older sister to Edith and Agnes. She is the deuteragonist of Despicable Me, one of the three tritagonists of Despicable Me 2 and one of the three tetartagonists of Despicable Me 3.
Margo is the oldest of the three orphan girls that Gru adopts. Before she was adopted, she was an orphan horribly treated by Miss Hattie. She, like her younger sisters, wished to be adopted by somebody who would love them. She is very disapproving of Edith's mischief, shown where Edith jumps in puddles which gets her and Agnes wet, and also when she breaks a vial of acid in Gru's kitchen.
She does join in with Edith's antics if it's against someone she doesn't like. She finds it very endearing when Agnes says innocent childlike things (although she does display mild irritation at Agnes' fixation with unicorns), the total opposite of Edith, who finds it irritating.
Margo is one of the three girls staying in Miss Hattie's Home for Girls. She tries to act hopeful to Miss Hattie, but when she reports to her the cookie sales, Miss Hattie is angry and warns Margo and her sisters that if they don't sell enough, they will be put in the Box of Shame. She, along with Edith and Agnes are adopted by Gru. At first, she dislikes him and refuses to accept him as her new father. However, she eventually learned to get along with him, who loved her in return.
Their relationship as father and daughter is broken briefly when Dr. Nefario sent her, Edith, and Agnes back to Miss Hattie and when she is later forced to jump from Vector's ship during a life-threatening situation. Once Gru rescued her, she thought of him as a father and told him she loved him.
The Social Worker telephones Gru´s house and Margo answers. Margo gets scared when the Social Worker tells her (making Gru´s voice) that he is coming to check if the house is good for children. Margo tells the girls and the Minions and they all help to turn the house appropriate. When the Social Worker arrives, she dresses herself as Gru (with a minion's help using Gru's clothes). The Social Worker says the house is appropriate for children, but then Gru arrives, the Social Worker faints at seeing two Grus at the time. Gru is happy for it, but he also faints when he sees his house looking girly.
During most of the ride until the anti-gravity recycling room, Margo controls a type of levitating hovercraft.
Despicable Me 2
Margo is seen texting a friend named "Avery" by Gru. Concerned that she might be talking to a guy behind his back, he asks her whether Avery is a boy or a girl.
At Paradise Mall, Margo encounters and falls for Antonio, the son of Eduardo, much to Gru's horror. Realizing their relationship, Agnes and Edith inform him that Margo has a boyfriend, who gets angry and tries to separate the two. Margo goes on a "date" with Antonio which is stopped by Gru.
At some point later, at the Cinco De Mayo party, Gru finds a depressed Margo, who tells him that Antonio is dancing with another girl and has cheated on her. Gru then freezes Antonio with a freeze ray in return as a depressed Margo leaves. Gru also told her, Edith and Agnes to stay home, because Eduardo was El Macho. While Margo was playing a unicorn board game with Agnes, they hear a strange growling noise, and it was Kevin.
Margo is watching a movie with her family when Dave's pet UFO suddenly destroyed the television because of the fictional UFO that it thought was real and was attacking them.
Margo is seen with Edith and Agnes when they hear an ice cream truck and head out on their bikes to get some ice cream, while Margo and Edith head down the street with the other kids not knowing that Agnes had falling off her bike, she and Edith are amazed when they see Agnes on her new bike and they all began to go down the road, the girls finally make to the ice cream truck however before they could get treated to some ice cream a robber comes out of the jewellery store and carjacked the truck with the ice cream and drives away.
Margo and the other kids watched the truck take off and then they all witness Agnes going after the thief Margo then gets worried about Agnes and they all follow her. After Agnes stop the Jewels Thief and saved the day Margo and Edith are enjoyed by the raining ice cream and cheer for Agnes, later Margo was sorry that Agnes' bike blow up but she didn't care as she said she like her other bike better, Margo and Edith are once again amazed as Agnes' bike transformed in robotic suit and they both watch her fly away.