Castore founder Tom Beahon has revealed the partnership with Rangers was "transformational" and helped built the brand into a $1bn sportswear empire.
The Liverpool company have produced Rangers kits from back in 2020. Castore also assist in retail operations at the club.
Castore work with huge clubs and athletes around the world with Andy Murray having been kitted out by the brand in the past.
The company supply Everton, McLaren Formula 1, Red Bull Racing, England Rugby and England cricket.
However, the partnership to produce Rangers kits is the standout collaboration for Beahon who branded the agreement as "transformational".
The reason for that is simple, according to Beahon, Rangers are a truly global brand with genuine backers around the world.
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Launched by pitching to personal trainers outside gyms, Castore has been labelled as a $1bn sportswear empire and legitimate competitor to Adidas and Nike.
Speaking on the Secret Leaders podcast, Beahon named Rangers as the partnership that "really made a difference" for Castore.
He explained: "There are a lot of clubs think they have a global fan base, there are not that many that do.
"Rangers Football Club was a transformational partnership, I would say.
"Globally recognised club and brand, genuinely global fan base.
"People might watch the Premier League in Taiwan, Vietnam and Cambodia and Mexico but they tend to support quit a small handful of teams.
"Rangers is one that people know all over the world. That was a big part of it."
