accounts/models.py


class Role(models.Model):

    ROLE_CHOICES = (
        ('agent', 'Agent'),
        ('agency', 'Agency'),
        ('manufacturer', 'Manufacturer'),
    )
    role = models.CharField(max_length=15, choices=ROLE_CHOICES)

    def __str__(self):
        return self.role


class User(AbstractUser):

    role = models.ForeignKey(
        Role,
        on_delete=models.CASCADE,
        blank=True,
        null=True,
    )

    def __str__(self):
        return self.username

    def save(self, *args, **kwargs):
        if not self.pk:  # the instance is created
            self.role, created = Role.objects.get_or_create(role="agent")
        return super().save(*args, **kwargs)