Which type of will must include the testator's signature and be written in their own handwriting?

A holographic will is a type of will that must include the testator's signature and be written in their own handwriting. This form of will is particularly significant because it does not require witnesses to be legally valid, as long as the essential components of a will are met. The testator's intent to create a will must be clear, and the entire document must be in their handwriting, including the signature, to ensure authenticity and to reflect their personal wishes accurately.

In contrast, a witnessed will typically requires the signatures of at least two witnesses who observe the testator signing the document. A codicil is a supplementary document that modifies an existing will and must also follow certain formalities, including signatures and sometimes witnesses. An amendatory will is similar to a codicil but is usually a complete replacement of an existing will, which also requires adherence to legal formalities for validity. Therefore, the distinguishing feature of a holographic will is its handwritten nature by the testator, setting it apart from these other types.