Sirzechs Lucifer

Sirzechs Lucifer (formerly Sirzechs Gremory) is a major character in High School DxD. He is the older brother of Rias Gremory, husband of Grayfia Lucifuge, and father of Millicas Gremory.

He serves as one of the Four Great Satans (Maou) ruling the Underworld, bearing the title Lucifer (specifically Satan Lucifer in charge of domestic affairs in earlier parts of the story). He is widely known as the Crimson Satan or Satan Red, and is regarded as one of the strongest devils in existence — a "Super Devil" with mastery over the Power of Destruction.

He appears as a handsome young man in his early 20s (despite being centuries old), with shoulder-length crimson hair and blue-green eyes, often described as looking like a male version of Rias. His personality is laid-back, kind, caring, protective (especially toward his sister), and somewhat goofy/perverted at times, though he becomes extremely serious and terrifyingly powerful when the situation demands it.

(Note: Some story events affect his exact status later on, but this covers his core role and identity in the series.)