Odin and the Runes
To win the runes, Odin hung himself on the world-tree Yggdrasil for nine nights, pierced by his own spear, until the runes revealed themselves to him [S1]S1 · Poetic Edda (Codex Regius)c. 1270 (preserves earlier oral poetry)textOpen source ↗. The runes are the source of wisdom and of the poetic art, and Odin is their patron [S1]S1 · Poetic Edda (Codex Regius)c. 1270 (preserves earlier oral poetry)textOpen source ↗[S3]S3 · Skaldic poetry (various)9th–13th c. CEtext.
The beliefs are pre-Christian (attested archaeologically from the Viking Age); the written sources are Christian-era (1220–1300) and post-hoc. The gap between belief and text is part of what this section presents.
The 'nine nights' and the details of the self-sacrifice are from the Hávamál (Poetic Edda); the act is a symbolic, not a literal, one [S1]S1 · Poetic Edda (Codex Regius)c. 1270 (preserves earlier oral poetry)textOpen source ↗.