She makes her first appearance on Metal Gear Solid and is of Chinese descent. In the game, whenever Solid Snake would save his game, she would usually give him a famous proverb from various Asian and Western authors and philosophers, such as "You must cross the river before telling the crocodile it has bad breath." She developed the Codec and Soliton radar system that Snake uses during his mission in Shadow Moses, and at the end of the mission creates a backup of Snake's mission progress at his request.
Although she's not seen in person, Mei Ling makes a voice-only cameo in the Tanker chapter of Metal Gear Solid 2, where Otacon handles data saving as well as attempting to give Snake proverbs much like she did. If the player saves their game a set number of times, Otacon will once more fumble a proverb causing Mei Ling to step in and tell Otacon off for not making better use of the proverb sheet she gave him, before properly explaining the proverb to Snake. Officially, Mei Ling lends assistance to the Philanthropy group that Snake and Otacon are part of.
Her final canon appearance is in Metal Gear Solid 4: Guns of the Patriots, where she is now the Captain of the USS Missouri, a former Navy vessel turned into a museum and then a Navy training vessel. When Liquid Ocelot takes control of the world's SOP-dependent weapons tech, the Missouri, lacking nanomachines and SOP tech, is the last bastion against Ocelot's Outer Haven battleship. Mei Ling captains the ship during the final battle between the Missouri's onboard army and Ocelot's army. After the crisis is over, she serves as a bridesmaid during Meryl Silverburgh and Johnny Sasaki's wedding.
She communicates to Snake via Codec and gives information about the fighters on the battlefield. She talks to Snake about Peach, Sheik, Toon Link, Zero Suit Samus, Pikachu, Lucario, The Ice Climbers, Marth, Lucas, Olimar, and Meta Knight.