Like Jaime Lannister in Game of Thrones, I would have never expected to like this guy judging by the first season.
He was a Holy Knight, and a druid. He and his best friend Dreyfus were corrupted by the demon Fraudrin. They murder Grand Master Zaratras and assume his role for about ten years. Plotting to take over Liones eventually.
He eventually becomes a synthetic demon, at a time, he becomes nominally stronger than Meliodas.
And Meliodas and the Seven Deadly Sins defeat him and his treason with a very impressive Revenge Counter attack.
He comes back and is human again. He joins the side of good. I really enjoyed watching him fight Fraudrin to free his friend.
And I’m glad he had a chance to make peace with Zaratras.
He remains somewhat important in the last story. Volunteering to serve the archangel Ludociel. He even offers to serve as his vessel which he somehow refuses.