This is one of those very-well-described mental models. I just felt inspired to look up its origin:
The earliest reference is by David Guest in 1991.[1] Tim Brown, CEO of the IDEO design consultancy defended this approach to résumé assessment as a method to build interdisciplinary work teams for creative processes. In the 1980s and probably earlier, the term "T-shaped man" was used internally by McKinsey&Company for recruiting and developing consultants and partners, both male and female by then.
This is one of those very-well-described mental models. I just felt inspired to look up its origin:
en.wikipedia.org/wiki/T-shaped_skills