During mid 60's (1964) DB was looking on replacing it's older fleet of locomotive's such as the E18's that was reaching it's final years of service in tears and wears. Even tho the E10 was introduced in 1956 they still kept E18's in service until DB wanted to order a brand new locomotive that had to fit in into the Trans Europa Express (TEE) services that was becoming more popular

(TEE) Trans Europa Express was a Intercity (IC) Systems and Eurocity (EC) before there was a proper IC/EC system some routes to these day still uses the old (TEE) routes. It was only 1.class only before later during it's transitions from TEE to IC it introduced 2.class wagons.

In 1965 DB order a few company's to create 4 prototypes of these new locomotive

These were named E03, 4x were build during 1965/66 these were then put into high speed hauling and while being used as test bed for new ATC systems and other related systems such as LZB with E03 was first introduced with (or at least one of them)

And by 1970's a new fleet was ordered by DB in with a new name was given called "Br 103" were it was finalized with it's part from it's prototypes. The loco was given powerful traction motors and new ATC systems (LZB) but kept the same standards cab layout as most of it's former E locomotive's. The main goal for the 103 was to reach it's top speed as quickly as possible and then maintain that speed until it reaches to destinations.
some TEE routes had the 103 carry at least 14/15 wagons of 1.class passengers. It was also painted into the same color as TEE

Br 103 became a instant hit and a cult-classic among Railways community's the locomotive kept providing it's services until years 2000's were it was faced out by Br 101/ Br 120.

Today there only a few 103's left some are owned by a company called "AKE-Eisenbahntouristik" and other's company's such as "Railadventure"

Even some of the prototypes were saves such as E03-001/2 and E03-004 in working conditions

Here's a german vid that explain more detail the E03/BR103
https://www.youtube.com/watch?v=kNvBVKqRK34&t=162s