Darrow was King Orlon Galathynius's lover for decades before the fall of Terrasen, and since Orlon's death, he has become a "cold, hard bastard, but still a fair one," according to Aedion. The only thing he saved from Terrasen during the Fall was the Kingsflame.
When Aelin returns to Terrasen in Empire of Storms, her and her court meet with Darrow, Murtaugh and Ren Allsbrook to discuss her return to Orynth and plans for the war with Erawan. However, the meeting does not go well. Aelin becomes angry at Darrow when he reveals that according to the laws of Terrasen, she is not actually queen. It is clear that Darrow wants to protect his country from the incredibly dangerous court of Aelin.
After the meeting, Darrow and Aelin part ways. Darrow returns to Orynth. Darrow does not believe magic will play a role in the upcoming war, since it did not make a difference when Adarlan invaded, and knows that men can win wars without it. Before Aelin leaves, Darrow bans her from setting foot in Orynth and tells her if she tries to take back her throne without the lords' invitation, it will be treated as the act of war it is.
Darrow is still his grumpy self, especially when wars are tough, but he is not so evil that he does not like Evangeline. Sending her out to be his messenger to distract her from the war, Darrow begins to think of her as something like a grandchild and asks Lysandra if Evangeline may become his heir. Lysandra agrees, and thus, he forms a deeper connection with Evangeline, asking her to be his heir as he didn't have any children of his own and he also wanted a heir for his hold.