EDIT: Many thanks to Nelson for helping me revise. Any remaining mistakes are my responsibility.
I was a hero, then I took an arrow to the knee.
Ic/æðeling: “Adventurer” is a French word, so I had a difficult time translating it. The closest approximations I could come up with were “hero” and “wanderer.” Since “wanderer” usually has an elegiac tone in OE, I went with “hero.” “Ic” and “æðeling” are both in nominative singular case.
wæs: “Wæs” is first person simple past tense, the only grammatical tense OE uses in the past tense. The simple past can encompass a number of meanings. While it is possible to use the verb “to use” as an auxiliary for the infinitive “to be,” such constructions in OE are technically adjectival, and the verb “to use” is only used in the sense that one would use a sword, so it would not be a good equivalent.
nom: On recommendation, I’ve used the first person of “nimian.”
þām cnēowe: The preposition “tō” is best used with the dative case to indicate “to” or “toward,” though considering dialectical differences, genitive case would be just as accurate. “Cnēo” declines as a strong noun; the definite article is declined accordingly.
I was a king, then I took an arrow to the eye.
The picture here is Harold Godwinson from the Bayeux Tapestry, the last Anglo-Saxon king who was slain by an arrow in the eye. The same rules apply here as above, save that “ēage” is a weak neuter noun of the –e ending class, which is declined the same as a strong neuter noun, save that the nominative and accusative cases are identical.