Which calculator manufacturer first introduced a graphing calculator that became widely adopted in mathematics education?

In the 1970s and 1980s, a fierce market battle emerged in the mathematical tools industry as electronic calculators began replacing slide rules and mechanical calculators. Companies competed aggressively with innovative features, dropping prices, and marketing campaigns targeted at students, scientists, and business professionals. This period fundamentally transformed how mathematics was taught and practiced worldwide.

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Texas Instruments (with the TI-81 in 1990)
Hewlett-Packard (with the HP-28 series)
Casio (with the fx-7000G)
Sharp (with the EL-5200)