The Lagann is Simon's personal Gunman which he finds in the first episode while digging tunnels in his village. It received its name, Lagann (羅顔), meaning "enveloping face", from Kamina and draws power from the Core Drill, a small golden drill Simon uses similar to an ignition key. In Gurren Lagann Parallel Works episode 8, it's revealed that the first Laganns were found by Lordgenome as a child during the Anti-Spirals' initial assault on Earth long before the series' story begins and as such were used as a basis in the creation of the all Gunmen that appear in the show to use against their enemies. However, after Lordgenome's betrayal he seemingly destroyed all of them except for the one that was placed deep underground until Simon finds it.
Unlike any other Gunmen in the series, the Lagann sports a unique cockpit and stands just short of an average human adult as opposed to the others which are all mostly the sizes of small buildings or larger. This physical handicap, in tandem with the usually average level of fighting spirit supplied to it by Simon, puts the Lagann at a considerable disadvantage in single combat against enemy Gunmen. However, when Simon is driven to give his best during combat the Lagann's power increases exponentially, giving it the unique ability to generate drills from nearly any part of its frame. Lagann's other and most notable power is the "Lagann Impact", its trademark ability to combine with other machines by piercing them with its drills. It's through this ability that the titular Gurren Lagann is created, along with the other more large-scale mechas in the series. It also can fly by using a small battery like object on its back.
- In the second movie it is implied that Lagann has its own sentience, when after the Anti-Spiral demolishes it it grabs Simon and throws him. Simon himself is surprised by this and yells out "Lagann!?" afterwards meaning he didn't tell it to do so.
- In both the TV series and the second movie, the crew of Super Galaxy Dai-Gurren find numerous Laganns deep within the Galactic Spiral Abyss. These Laganns are then used as the cockpits of Tengen Toppa Gurren Lagann as well as the other Tengen Toppa Gunmen. After the Anti-Spiral universe is destroyed and all of the Spiral Power maintaining the Tengen Toppa mecha vanishes, the pilots are still inside their Lagann cockpits.
- Lordgenome possesses a different type of Lagann, which acts as the head of the Lazengann. It is black, it has a slightly different face, and its canopy is a simple red force field, rather than the typical brain-pattern canopy.
- In the final charge against the Anti-Spiral race, Lagann is seen having the same spiral eyes as Kittan and Lordgenome.