Megatron has had a lot of different alt-modes over the years, so the answer depends on which version you mean, but the most iconic are:

  • In the original G1 cartoon and early comics, Megatron transforms into a Walther P38-style handgun.
  • In many later series, especially from the 1990s onward, he most often turns into a tank, emphasizing heavy firepower.
  • In several continuities (like the live‑action movies and some cartoons), he also transforms into various jets or Cybertronian flying vehicles.
  • Across different shows, toys, and comics, he’s additionally been depicted as a particle-beam cannon, a Cybertronian jet, a truck, a T‑Rex (Beast Wars), a spaceship, and even a Formula 1 engine.

So if you’re asking generally “what does Megatron transform into,” the safest short answer is: he’s most famous for transforming into a gun in G1 and a tank in many modern versions, with jets and other heavy-combat vehicles as frequent alternatives.