A navy-armored robot with an X-shaped scar on his face, Axl has the unusual ability to take on the appearance and abilities of any reploid he defeats, an ability that is initially unique. Axl is also armed with a pair of handheld blaster pistols (although, in most cases Axl only uses one), which he calls Axl Bullets, and the ability to hover in midair and roll through enemy shots.
Axl was introduced in Mega Man X7, having just left the mercenary Red Alert Syndicate and seeking asylum and membership in the Maverick Hunters. The Red Alert Syndicate, which hunts Mavericks and also takes on less savory assassination jobs, has been infiltrated by Sigma, and confronts the Maverick Hunters. X, Zero, and Axl work together to defeat Red Alert, but in so doing, destroy both Red, the leader of Red Alert, and Sigma, the only ones Axl knows of who know about his origins. In Mega Man X: Command Mission, Spider, a mysterious reploid who fights alongside X, Zero, and Axl, also has a similar ability.
Mega Man X8 revealed that Axl is a prototype for a next-generation reploid. These next-generation reploids all have the ability to copy other reploids, as well as a chip that prevents them from going Maverick. These next-generation reploids are pawns in two different plots:
- With the copy chip containing a copy of the Sigma virus, which removes all safeguards and gives them the freedom to go Maverick at will, Sigma wants to destroy the old world and start a new age with his "children".
- Lumine, leader of the next-generation reploids, and on whom all of the next-generation reploids are based on, also plans to use them to destroy all the humans and old-model reploids so he can repopulate the Earth with next-generation reploids. X, Zero, and Axl defeated them both, but when Lumine was defeated, he lashed out in his death throes, cracking the crystal on Axl's head. Axl's ultimate fate was unknown. However, seeing as how he is in fine form in Command Mission, he was obviously repaired.
- In Mega Man X8, Axl may acquire upgraded armor by performing certain tasks, transforming into "White Axl". Axl's armor is a mix of purple and white, and it reduces the damage that he takes, gives him longer dash distance, and allows him unlimited hover time while shooting in mid-air. Also, the X-shaped scar on his face is gone, and he resembles Lumine, the reploid he was patterned after, greatly.
- Although the Biometal Model A appearing in Mega Man ZX Advent is heavily implied to be based on Axl, using twin pistols and carrying the A Trans ability, it is instead based on Master Albert, which creates some speculation about Master Albert's origins.
- Axl made a cameo appearance in Zero's ending in Tatsunoko vs. Capcom: Ultimate All-Stars.