Marshall King is the creator of NTX Open H2O, a a website with information on open water swimming training and racing in Texas, New Mexico, Oklahoma, Arkansas and Louisiana. He joined Team in Training in 2003 and trained as a racewalker to walk his first half marathon, Virginia Beach Rock N Roll Half. He continued walking half marathons and full marathons. 18 months, he walked his first ultramarathon, The Heartland 50 mile ultra and began walking ultramarathon distances from 50k to 100 miles. In November, 2005, he became the 61st American to walk 100 miles in 24 hours (100.2 miles in 23:42) and became a Centurion.
A couple of years later he transitioned to running and continued to run mostly ultra distance events and began coaching for Team in Training, first as a walking coach, then as a run/walk coach.
In 2009 he raised money for the Prostate Cancer Foundation by running seven ultramarathons in seven months. After completing his final ultra, he took a break from running and entered physical rehabilitation. During this time, he began swimming as low-impact cross training and began to participate in open water swim training and races with a current interest is in 5 km distances and greater.