I'm torn between
Tate, J. Endomorphisms of Abelian Varieties over Finite Fields, Invent Math 2, 1966, p. 134-144
Lubin, Jonathan; Tate, John. Formal complex multiplication in local fields. Ann. of Math. (2) 81 1965 380--387.
Drinfelʹd, V. G. Coverings of $p$-adic symmetric domains. (Russian) Funkcional. Anal. i Priložen. 10 (1976), no. 2, 29--40. bearing in mind that, as I recall, the English translation is only 7 pages long.
Longer than some of those above, perhaps; but maybe they win on "importance."