Yoga was practiced before the ages of Mahabharata. Before Yajnavalkia. Before Patanjali. Before Thirumoolar. They are not the founders.
Not to speak of the authors of Hatha Yoga pradeepika, Gheranda Samhita or Siva Samhita which belong to 12th Century or later.
In Thirumanthiram, it is said that Lord Siva was the founder of yoga.
In Hatha Yoga pradeepika, Siva samhitha and Gheranda Samhitha also mention Lord Siva as the founder.
For those who could not accept this, we may conclude that ancient sages were the founders of Yoga.