Samuel L. Caster founded Mannatech in 1993, building a multi-level marketing firm that sells plant sugars. The company, which charges distributors up to $3,800 for starter packs, has faced federal investigations and multi-million dollar settlements over nearly three decades. Today, co-CEOs Stephen D. Fenstermacher and Robert A. Sinnott lead the company, which operates in 20 countries, including the US, UK, Canada, and Australia.

In 2005, Mannatech stockholders sued the company. They discovered Mannatech permitted sales associates to make false health claims about its products. The case settled three years later for $11.25 million. Mannatech denied any wrongdoing in the settlement.

That same year, Texas Attorney General Greg Abbott began an investigation. On July 5, 2007, he formally charged Mannatech, Caster, and related entities with running an illegal marketing scheme. The company settled in 2009. It paid $4 million directly to customers and $2 million to Texas to cover investigation costs. Caster personally paid $1 million and agreed to stay away from the company for five years.

The legal actions damaged Mannatech's finances. The company reported $32 million in profits in 2006. By 2008, it posted a $12.6 million loss. Losses grew to $17.3 million in 2009. Mannatech lost a quarter of its sales by mid-2010. The S&P 600 Index removed Mannatech, stating it no longer represented the small-cap market space.

Mannatech built its business on unproven medical claims. Sales associates promoted glyconutrients, branded plant sugars, as cure-alls while the company did not intervene. After the settlements, Mannatech appears to have tightened controls. But trust remained broken.

Mannatech survived these fraud allegations. Most multi-level marketing companies would have collapsed under such pressure. Mannatech restructured and continued its sales.

The company's product line consists of health supplements. These are built around glyconutrient science, Mannatech's claim that plant-derived sugars improve human health. The scientific validity of this claim remains contested. Mannatech charges premium prices for these products, with distributor starter packs costing up to $3,800.