Both catalytic activity and polymer molecular weight are two crucial parameters in olefin polymerization catalysis. Differed from the superior feature of early transition metal catalysts, late transition metal nickel catalysts are usually more challenging to approach both of them at an ultrahigh level. In this contribution, by use of a concerted double-layer steric strategy a new conceptual alpha-diimine nickel catalyst was prepared to address the issues. The nickel catalyst featured highly thermally robust (0-150 degrees C), was ultra highly active (a new level of 1.03 x 10(9) g mol(-1) h(-1)) toward ethylene polymerization, and simultaneously produced ultrahigh molecular weight polyethylene product (UHMWPE, M-w = 4.2 x 10(6) g mol(-1)). Additionally, these obtained polyethylenes featured linear (2/1000C) to lightly branched (32/1000C) and could also be incorporated with a small amount of methyl 10-undecenoate. (C) 2020 Elsevier Inc. All rights reserved.