Introduction:
Chordates are a group of animals that possess certain characteristics during their development or at some point in their life cycle. These characteristics are known as chordate characters. Among the given options, the vertebral column is not an essential chordate character.

Explanation:
The essential chordate characters are as follows:

Notochord:
- The notochord is a flexible rod-like structure that is present in the dorsal part of the embryo.
- It provides support and acts as a precursor to the vertebral column in most chordates.
- The notochord is present in all chordates at some stage in their life cycle.

Pharyngeal Gill Slits:
- Pharyngeal gill slits are openings found in the pharyngeal region of chordates.
- These slits are used for various functions such as respiration, filter feeding, and sound production.
- In some chordates, these slits develop into gills, while in others, they may develop into other structures like the jaw or inner ear.

Dorsal Hollow Nerve Cord:
- The dorsal hollow nerve cord is a tubular structure that runs along the dorsal side of the body in chordates.
- It is derived from the ectoderm and eventually develops into the central nervous system, including the brain and spinal cord.

Vertebral Column:
- The vertebral column, also known as the backbone or spine, is a series of vertebrae that protect the spinal cord in vertebrates.
- It provides structural support and flexibility to the body.
- While the vertebral column is present in most chordates, it is not an essential characteristic of chordates as it is absent in some groups such as tunicates and lancelets.

Conclusion:
Among the given options, the vertebral column is not an essential chordate character. The essential chordate characters include the notochord, pharyngeal gill slits, and the dorsal hollow nerve cord. These characters are used to classify animals into the chordate group.