The E.636 was an electric mixed-traffic locomotive designed by Alfredo d'Arbela for lines electrified with 3 kV DC and with tight curves. Like the preceding E.626 it had three two-axle bogies, but the body was split into two halves. Its top speed was still 95 km/h and the power had been increased from 1,850 kW in the last batches of the E.626 to 2,100 kW. Later the E.646 and the E.656 were developed as successors to the E.636.

The first batch of the E.636 consisted of 108 locomotives which were built between 1940 and 1942. 135 more were built between 1952 and 1956. The last and largest batch of 226 was built between 1957 and 1962. This resulted in a total of 469, making it the most numerous electric locomotive class of the FS. 19 had a different gear ratio for a top speed of 120 km/h. The top speed of the others was increased to 105 km/h in 1948 and to 110 km/h in 1982.

In the nineties, the tasks of the E.636 shifted to mainly freight service. In 1996, it became clear that the position of the driver did not offer any safety in the case of a crash. So 200 were rebuilt to address this problem and additionally, the comfort, climatization and insulation of the cabs was increased and all asbestos was removed. All were withdrawn in May 2006 and eleven were preserved.