This is from M. Puzo's The godfather.
On the night before the shooting of Don Corleone, his strongest and most loyal and most fearest retainer prepared to meet with the enemy. Luca Brasi had made contact with the forces of Sollozzo several months before. He had done so on the orders of Don Corleone himself. He had done so by frequinting the nightclubs controlled by the Tattaglia Family and by taking up with one of their top call girls. In bed with this call girl he grumbled about how he was held down in the Corleone Family, how his worth was not recognized.
I didn't get the point of the last sentence, especially the part that I emphasized. Hold sth down means to keep something at low level. Was Luca Brasi one of the most important person in the Corleone's bussiness? I think so.