Pharmaceutical companies and their brands changed as regularly as the wind direction. However, to the best of my understanding, at present this is the ownership of the largest USA levothyroxine and desiccated thyroid brands:
AbbVie owns the Synthroid branded levothyroxine.
Allergan owns the Armour branded desiccated thyroid. (Through its acquisition of Forest as part of Actavis.)
However, AbbVie now own Allergan.
Hence, both Synthroid and Armour are owned by one gigantic pharmaceutical company.
In June 2019, U.S. pharmaceutical company AbbVie announced it had reached an agreement to acquire Allergan for $63 billion. The merged company would be domiciled in the U.S. for tax purposes.
en.wikipedia.org/wiki/Allergan
AND
abbvie.com/abbvie-allergan-...
Just to confuse a little more, Synthroid is manufactured by Mylan in Canada for "rest of world" distribution - excepting USA.
In late July 2019, Mylan and Pfizer announced that Pfizer would spin off and merge its off-patent medicine division, Upjohn, with Mylan, forming a brand new pharmaceutical business with sales of around $20 billion.[94] The new company will be called Viatris, a name held by one of Mylan's subsidiaries.
Apologies. I didn't mean to give you a headache.