On MyBankTracker.com we introduced a new category structure. For reasons I won't get into, I needed to find the parent category of the current post's category. But, finding the parent category was surprisingly difficult using standard Wordpress functions. Anyways, this code is based on get_category_parents() which can be found in wp-includes/category-template.php. Note: this is tail recursive, so it could be rewritten to be iterative. Feel free to copy and redistribute.

Usage:

As expected, use this code at your own discretion. No support or liability implied by sharing this.