Different people in auto accident cases are referred to by different labels for legal reasons. Given that you're probably not a car accident attorney, it can be helpful to have a guide to the cast of characters who might appear in your case.
This is generally going to be the driver who suffered injuries in the incident, but there are exceptions. A passenger might pursue a claim against the driver they were with if they feel their injuries were the product of the driver's actions. There are also cases where your insurance company may stand as the plaintiff rather than you, especially if they already paid out your claim and are pursuing legal action against a different insurance carrier. Most of the time, though, it's going to be you, the person who was injured, seeking a claim against an insurance carrier or a self-insured organization.
The defendant is the person being accused of causing the accident or the party you're seeking money from. A car accident lawyer will typically go after the operator of the vehicle that hit your ride, although the claim may be handled by their insurance company. One possible exception is if the at-fault party was doing work for a business, an organization, or a government agency at the time. In those cases, their employer is likely to be named as the defendant because they would be seen as a fleet operator. Also, to be realistic about how claims work, the employer is probably better insured than the driver. Similarly, if it comes to a trial, juries tend to be more sympathetic to individuals than organizations, so the optimal choice is probably suing the company.
If an insurance carrier receives a claim in the case, they will assign an adjuster. This person will assess what happened and compare it to similar incidents the insurance company has handled. If the adjuster believes the claim is unjustified, they will reject the claim. Conversely, if the claim appears to be reasonable, the adjuster will send you or your car accident attorney a settlement offer.
Medical Professionals and First Responders
Reports from doctors, police officers, and on-scene EMTs carry a lot of weight in car accident cases. They make excellent witnesses because neither the court nor opposing counsel is likely to question their testimony. Likewise, they probably have experience dealing with accidents, and that means they can provide compelling explanations of what they saw and how events appear to have unfolded. Get their names ASAP if you speak with any medical professionals or first responders.
Speak with your car accident lawyer if you need more information.