Cringer

There is only one animal. Cringer is what he is most of the time: green, orange striped, roughly the size of a large tiger, and reluctant to leave a warm spot on the floor. Battle Cat is what he becomes when Prince Adam transforms into He-Man and turns the Sword of Power on him. The transformed version is bigger, armored, and fearless.

The pairing is a deliberate mirror of Adam and He-Man. Adam is idle and useless in public so that nobody suspects him; Cringer is a coward for the same structural reason. Both drop the act at the same moment, in the same scene, by the same mechanism. Neither can do it alone, and Cringer cannot trigger the change himself.

Clipped from our own copy of He-Man and the Masters of the Universe, House of Shokoti Part I of II (1983), 1:27 to 3:05, 1 minute 38 seconds. Nothing is added and nothing is sped up. Copyright Mattel.

Battle Cat came first. In the 1982 Mattel toy line and in the earliest Donald F. Glut minicomics there is no Cringer at all. Battle Cat is simply a wild tiger who lives in the jungle and comes when He-Man calls him. There is no dual identity, no Prince Adam and no transformation.

The Cringer alter ego came from DC Comics in 1982, in Paul Kupperberg's "From Eternia, With Death!", a Superman team-up in DC Comics Presents #47 that pairs the tiger with Prince Adam a year before Filmation went to air. What the Filmation cartoon added was the sword-beam transformation sequence and the running comic relationship between Adam and his frightened pet, which is what fixed the character in most people's memories.

Yes, in the series most people remember, and this varies more than you would expect:

Filmation, 1983, talks throughout. Alan Oppenheimer voiced Cringer's nervous mumbling and Battle Cat's gruffer register. 200x, 2002, does not speak at all; Cringer makes house-cat noises and Battle Cat roars, using real big-cat recordings, with no credited voice performer for either form. Netflix CGI, 2021, talks again, with David Kaye voicing both forms. Revelation and Revolution keep him talking, voiced by Stephen Root.

Filmation gave the character a proper origin in the 1984 episode "Battlecat." A young Adam rescues a green tiger cub from a saber-cat. Teela and the other children mock the cub for being frightened and call him a cringer, and the name sticks. Years later, after Cringer accidentally sees Adam transform, He-Man points the sword at him and Battle Cat exists for the first time.

Both forms had already appeared on screen before that, in "Diamond Ray of Disappearance," which aired on September 5, 1983 as the first episode of the Filmation series. Episode lists often label it S01E04 because it was fourth in production order, but it was written as the audience's introduction and broadcast first, so viewers had known both forms for more than a year by the time the origin episode aired.