Atenulf I (died 910), called the Great (Latin magnus), was the prince of Capua from 7 January 887 and of Benevento from 899, when he conquered that principality.
The son of Landenulf, gastald of Teano, Atenulf, through his influence and conquests, succeeded in vindicating his Lombard family's pretensions to princely status, à la those of Benevento and Salerno.
From 879, Capua had been contested between several candidates, but, by 887, Atenulf had removed his brothers and cousins from contention and become sole prince with the assistance of the hypatus Athanasius of Naples.
Atenulf then turned his attention to Benevento, which had recently been under Byzantine and then Spoletan control.
Atenulf allied with Amalfi and Gregory IV of Naples and attacked and defeated the Saracens in 903.