From Bulbapedia, the community-driven Pokémon encyclopedia.
Team Rocket grunts act as fodder, enforcers, workmen, crooks, and backup for various leaders in Team Rocket.
In the games
In the games which they appear, a Team Rocket Grunt is considered a class of Pokémon trainer. Their designs varied a bit through the generations.
In Generation I, there are only male Rockets. They are depicted as adults wearing black caps on their heads and black uniforms with a big R on their chests. They each hold a whip. The later generations don't use whips.
In Generation II, female Rockets start to appear. The males' design isn't changed much. Their uniforms and caps look the same, but the whips are absent. They also appear to be a bit younger than the grunts from Generation I. The female grunts are depicted as red haired women in white Team Rocket uniforms without caps. Their design is very similar to Cassidy's.
In Generation III, the designs of grunts change more distinctly. The males are depicted as teens in the black Rocket uniforms. The uniform's look is different, such as with a smaller R on the front, and the cap is shaped differently. The females look completely different than their predecessors from Generation II. They are depicted as short haired teens wearing black (not white) uniforms and black caps just like the male grunts. Both the male and female grunts' hair is colored green on the Sugimori artwork. However, on the game sprites from Pokémon FireRed and LeafGreen, the female's hair is definitely red and the male's hair isn't clearly seen.
In Pokémon Red and Blue and Pokémon FireRed and LeafGreen, the grunts are found in Mt. Moon going after Fossils. In Cerulean City, one grunt is at the end of the Nugget Bridge recruiting for Team Rocket, and another had stolen a TM.
In Celadon City, the grunts operate a base under the Game Corner trafficking Pokémon all over the world.
Team Rocket murders the mother Marowak in Pokémon Tower as part of a plan to steal Cubone and sell their skulls. This upset the mother Marowak's spirit. When Mr. Fuji finds out about this, he goes to the tower to confront the Rockets and is taken captive, but is later rescued after the player calms mother Marowak's spirit and drives the Rockets out of Pokémon Tower.
They make their final appearance when they take over the Silph Co. headquarters. After the player defeats them there, Giovanni disappears, later reappearing at his own Viridian Gym, and the grunts are not seen after this.
However, there are still two grunts that can be seen in Pokémon FireRed and LeafGreen after Giovanni's defeat. They are in Celadon City and can be found in an old man's house next to the restaurant. However, they will never leave, nor will they battle you.
In the Sevii Islands
In Pokémon FireRed and LeafGreen, grunts are found on several of the Sevii Islands. On Island One, the player faces two in front of a cave which leads to the Ruby for the Net Center. On Island Four, the player helps Lorelei, who nearly defeated a grunt with her Lapras's Ice Beam. On Island Six, there is a grunt in front of Altering Cave. In the Ruin Valley, a Rocket scientist steals the Sapphire from the player. On Island Five, the player finds a group of male and female grunts operating from a warehouse obtaining a large number of Pokémon, most of them rare, and trying to make a working prototype of the high-frequency sound wave machine which would influence evolution; after the player defeats the grunts and the two administrators, they will pull out, but not before telling the player that they will find Giovanni and restore Team Rocket. They have not been seen in the islands since.
In the Generation II games, three years after the events in Red/Blue and Fire Red/Leaf Green, a group of Rocket grunts operating out of Slowpoke Well take Slowpokes and cut off their tails to sell.
At Mahogany Town, the player finds a base underneath a shop in which the Rockets have been using a fully-working high-frequency sound wave machine that influences Pokémon evolution. The player works with Lance to stop them.
After winning the Glacier Badge, Professor Elm telephones the player and tells him or her that in a final attempt to contact their former leader, the Rocket grunts took over the Radio Tower in Goldenrod City, and the Radio Director was revealed to be a Rocket executive. The player must then travel to Goldenrod City Tunnel where the grunts were hiding the real Radio Director, who gives the player a card key that will access the third floor of the Radio Tower. It is here that the player is able to defeat the Rocket grunts and executives. Apart from a grunt stealing part of the Power Plant in Kanto, grunts are not seen after this defeat.
In the anime
In the anime, the grunts have had few appearances. They first appear in Battle Aboard the St. Anne, under the command of Jessie, James, and Meowth, trapping trainers and trying to steal their Pokémon.
In Johto, they operate around the Lake of Rage under the command of Professor Sebastian and Tyson to help in Project R; the project's goal is to force Pokémon to evolve artificially, thus giving the group powerful Pokémon to use. Later, operating from a under sea base, grunts are under the command of Namba, Butch, and Cassidy, attempting to harness a Lugia and its child.
They also appear in copious amounts during Mewtwo Returns, led by Giovanni and Domino, to capture Mewtwo and build a new Rocket Base on Mount Quena. However, they are all transported away from the mountain at the end of the movie.
They have also been seen helping Butch and Cassidy with their stadium scam in AG175. There, they were disguised as several tournament officials.
Team Rocket grunts have been known to use the following Pokémon:
In the manga
The grunts try to find Mew so that Team Rocket can finish development of Mewtwo.
Searching Mt. Moon, a group of grunts tries to find a Moon Stone for Team Rocket's use.
The grunts go after Blue, hoping they can get back a disk containing information on Mew.
The grunts try to capture Mew, but Red and Blue interfere.
The grunts are sent to catch Articuno.
An army of grunts is sent to take out Blaine, who left Team Rocket due to the creation of Mewtwo. After Red helps Blaine escape, the grunts use Moltres that they captured on the Indigo Plateau; Red defeats it with an Aerodactyl that he brought back to life.
As a part of the Saffron City invasion, the grunts use a Mr. Mime to put a Light Screen over the city; Red and Green, however, manage to get into the city.
The grunts try to get out of Saffron City because of the fight between Red and Green and Koga. The Gym Leaders not aligned with Team Rocket block all the exits, keeping the grunts in.
The Cinnabar Island base is destroyed by Mewtwo, taking out the grunts and scientists that work there.
The grunts as well as the Team Rocket Elite Trio were reorganized under Mask of Ice and given the name Team Rocket Neo.
The grunts are sent to cut the tails of Slowpoke living in the Slowpoke Well, but Silver stops them.
Chapters 108 and 109
Grunts, along with the two sub-leaders, Shum and Cart, are sent to destroy the Tin Tower, and are successful. However, they then lose a battle with Gold and Silver.
Cart gives a speech telling the grunts that it is time for the public to officially learn about the return of Team Rocket.
The Elite Trio and the grunts ride a train to the Indigo Pleateau.
Grunts intrude upon the Gym Leaders' exhibition match.
Grunts are put under mind control by Mask of Ice. Although the Elite Trio were saved from the mind control by Lt. Surge, they are told by him to help free the other grunts from the Mask of Ice's mind control.
Grunts are sent to retrieve the Rainbow Wing and the Silver Wing.
The grunts on the train to the Indigo Plateau are knocked out as Red and Green travel to fight Mask of Ice. Chuck tells the pair that the grunts will be taken care of.