The greatest king of the Gupta dynasty is believed to be Samudragupta because the Gupta Empire reached its greatest extent under his rule.
For further reading check the following articles:
|100 Differences Between Articles||UPSC Prelims|
|NCERT Medieval Indian History Notes UPSC||UPSC Mains Questions (2013-2019)|
|NCERT Ancient Indian History Notes UPSC||NCERT Modern Indian History Notes UPSC|