Éomund

History
Éomund was the husband of Théoden's sister, Théodwyn With her, they had two children: a son named Éomer (born TA 2991) and Éowyn (born TA 2995). When his children were very young, Eomund had been slain by Orcs.

The Two Towers
After his death, Éomund's body was taken to his family Soon later, Eomund's wife, Lady Théodwyn, died of grief. Théoden adopted Éomer and Éowyn and raised them alongside his son, Théodred.

Though Éomund was no longer living, his name was mentioned when Gríma Wormtongue formally addressed Éomer as "son of Éomund" when he had been banished from Rohan by Théoden, while under the influence of Saruman.

Théoden later mentions his brother-in-law's death to Aragorn, recounting this had been the first time he's seen Éowyn happy.

Éomund posthumously became the father-in-law of Faramir and Lothíriel through their marriages to Éowyn and Éomer and grandfather of Elboron and Elfwine.