Some cars leave a paper trail; the Lotus 38 left a name and a place in Lotus's list. What follows is what can be said with a source behind it. Its designer of record is Colin Chapman / Len Terry.
Where it came from
The Lotus 38 was the first rear-engined car to win the Indianapolis 500, in 1965, driven by Jim Clark. It was run by Lotus at Indianapolis from 1965 to 1967; a total of 8 were built, most for use by Lotus, but several were sold for use by other drivers, including A. J. Foyt and Mario Andretti.
Under the skin
it is rated at 500 hp. Kerb weight is 612 kg. Power-to-weight lands near 817 horsepower per tonne, which is hypercar territory, where the limiting factor is the tyre, not the engine. The wheelbase is 95.9 in. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
In context
Where it sits in Lotus's history is not in doubt: the Lotus 34 came before it; the Lotus 42 followed it. Nearby in the Lotus catalogue sit the Lotus 100T and the Lotus 101.