WordPress.org is open source software, which means it is developed and maintained by a network of volunteers. This means that no one owns WordPress, but the WordPress trademark and the WordPress.org website is owned by the WordPress Foundation, a non-profit organization.
WordPress.com is owned by a privately held company called Automattic. Automattic was started by the co-founding developer of the open source WordPress software, Matt Mullenweg. He started the company in 2005, two years after WordPress, with the main purpose to make WordPress hosting easier and allow people with little technical knowledge to start a blog with WordPress.