Lagann is a Gunman found by Simon 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 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.
Lagann has an ability that lets it combine with other gunmen. This ability is displayed first when Lagann and Gurren combine to form Gurren Lagann, but also when Lagann combines with the Dai-Gunzan to form the Dai-Gurren. Lagann's combining ability appears to transfer to Gurren Lagann, as the combined mech was able to capture the Cathedral Terra, transforming it into the Super Galaxy Gurren Lagann.
- 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.
- If it is not actually sentient, it is theorized that the spirit of Kamina was the one that possesses Lagann for a brief amount of time.
- 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.
- "Lagan" in English is a term for goods which have been lost to the bottom of the sea, but are recoverable. This can refer to how Simon and Kamina discovered Lagann deep within the desert.