Sigewulf

3. Ended up taking on dangerous challenges at least in part because those fathers were both having their reason and good judgment manipulated by opponents (Théoden through the treachery of Gríma/Saruman and Denethor by the selective truths shown to him by Sauron in the palantír).

4. Got killed in a battle where their opponents were targeting them to the exclusion of others around them (Saruman’s forces at the Isen were told to kill Théodred at all costs even while “disregarding” others, and the orcs at Parth Galen fire their arrows “always at Boromir” while leaving Merry and Pip untouched).

5. Were trying to summon aid at the time they were struck down (Théodred is shouting “To me, Eorlingas!” to summon reinforcements when he’s fatally wounded. Boromir blows his great horn to alert the rest of the fellowship before he’s brought down).

6. Took massive injuries but lived long enough afterward to pass on last words in which they invoke the names of the men who will come to replace them as leaders and express the hope that those next leaders will achieve victory (Elfhelm and Grimbold believe Théodred is dead before they discover he’s still breathing just enough to say, “Let me lie here to keep the fords til Éomer comes.” Boromir, as we all know, lays there with those arrows in his chest long enough to be found by Aragorn, at which point he says, “Farewell, Aragorn. Go to Minas Tirith and save my people.”).

7. Died within hours of each other (Théodred on the night on February 25 and Boromir around midday on the 26) at the same age of 41 because, oh yeah, they were also born within months of each other.

8. Didn’t get a burial/funeral in keeping with their status and the traditions of their people because they died in awful circumstances far from home (Théodred dies and is buried by Elfhelm and Grimbold’s companies at the fords rather than in the barrows outside of Edoras with his ancestors. Boromir is sent over the falls by the three hunters instead of laying in Rath Dínen with the other kings and stewards of Gondor).

9. Mentored and protected little brother-type figures (Faramir as Boromir’s actual little brother and Éomer as Théodred’s cousin/adopted little bro) who would go on to achieve what they were unable to do themselves while alive.

10. Died unmarried and childless despite being extremely marriageable, in the primes of their lives and presumably expected to produce another heir. (There’s an explanation given for Boromir—he’s not into women and prefers fighting and arms—though there is none for Théodred.) (Like many other people, I have my own personal HC for Théodred’s romantic life, but that’s for another day.)