A lesser known and currently obscure heresy, Monothelitism teaches that Jesus has two natures (divine and human) – which is correct – but that he only has one will.
Monothelitism was pronounced a heresy at the Third Council of Constantinople in 1681.
To explain why this teaching is heretical, it’s necessary to explain the Church’s orthodox position as articulated by the Christological definition of Chalcedon (it’s adopted by nearly every segment of the church that isn’t overtly schismatic). The orthodox position is that Christ has two natures (divine and human), but that it comes together in “hypostasis” in the “hypostatic union.” However, those holding to Monothelitism reject the claim, and instead hold that the two natures of Christ become one.
There are few practitioners of Montheletism today.