A transsexual is best described as:

The term "transsexual" is best defined as someone who identifies with a different sex than the one assigned at birth. This identification may involve a desire to transition, which can encompass various forms of social, medical, or legal changes to align their outward appearance and identity with their gender identity. It is important to recognize that being transsexual focuses primarily on the gender identity aspect rather than solely on physical changes or medical procedures.

The other options emphasis distinct aspects that do not encompass the full meaning of transsexuality. For instance, identifying with the assigned sex does not align with the experiences or identity of a transsexual individual. Limiting the definition to only those who undergo surgery excludes many individuals who identify as transsexual but may not pursue surgical options for various personal, medical, or financial reasons. Lastly, changing one's name legally, while often a step in the transition process, does not alone indicate a person’s gender identity or status as transsexual. Thus, option B appropriately captures the essence of being transsexual.