We study reals with infinitely many incompressible prefixes. Call A∈ 2ω
Kolmogorov random if (∃∞ n) C(A↾ n)> n-(1), where C denotes
plain Kolmogorov complexity. This property was suggested by Loveland and studied by
Martin-Löf, Schnorr and Solovay. We prove that 2-random reals are Kolmogorov
random. Together with the converse—proved by Nies, Stephan and
Terwijn [NST]—this provides a natural characterization of 2-randomness in
terms of plain complexity. We finish with a related characterization of 2-randomness.