Yolanda of Flanders

She was the sister of Henry of Flanders, the second emperor, who died in 1216. There was a brief period without an emperor, before Peter was elected; Peter sent Yolanda to Constantinople while he fought the Despotate of Epirus[?], during which he was captured. Because his fate was unknown (although he was probably killed), Yolanda ruled as regent. She allied with the Bulgarians against the various Byzantine successor states, and was able to make peace with Theodore I Lascaris of Nicaea, who married her daughter. However, she quickly died, in 1219.

She was succeeded by her second son Robert of Courtenay because her first son did not want the throne. As Robert was still in France at the time, there was technically no emperor until he arrived in 1221.