Please expand.
Logical relations appear to have been discovered in the 1970s.
The most famous instance is the report of [Plotkin 1973], where they are used as a way of characterising which functions can be expressed in -calculus.
In the report Plotkin credits the idea of using relations to Mike Gordon. He also points out that the first instance of using something akin to a logical relation for proving the equivalence of programs occurs in Robert Milne's 1973 thesis [Milne 1973].
Plotkin, G. D. ‘Lambda Definability and Logical Relations’. Memorandum. University of Edinburgh, 1973. [pdf]
@techreport{plotkin_lambda_1973,
type = {Memorandum},
title = {Lambda {Definability} and {Logical} {Relations}},
url = {https://homepages.inf.ed.ac.uk/gdp/publications/logical_relations_1973.pdf},
number = {SAI-RM-4},
institution = {University of Edinburgh},
author = {Plotkin, G. D.},
year = {1973},
}
Milne, Robert. ‘The Formal Semantics of Computer Languages and Their Implementations’. University of Cambridge, 1974. [link]
@phdthesis{milne_1974,
title = {The {Formal} {Semantics} of {Computer} {Languages} and {Their} {Implementations}},
url = {https://www.cs.ox.ac.uk/publications/publication3763-abstract.html},
school = {University of Cambridge},
author = {Milne, Robert},
year = {1974},
note = {Distributed by the Oxford Programming Research Group as Photocopy PRG-X13.},
}