Saint Jalmack is a World Noble who was introduced 10 years prior to the start of the series.

Though his initial appearance is hidden in the shadows, Jalmack has a similar hairstyle as the Roswald family, but his goes up in two bulbs. He also has a wide chin.

As with all other World Nobles, Jalmack wears a thick suit adorned with medal-like knobs on the front. However, since he was not at Sabaody Archipelago, he cannot wear one of the resin bubbles as a helmet, due to the bubbles popping outside of that area. Instead, he wears a rectangular helmet, in order to prevent himself from breathing the same air as commoners.

(Source: One Piece Wikia)