Looking for an evental replacement for their extensive F-4 Phantom fleet, Iran was an early partner (and major finacier) of the development of the F-15. The Imperial Iranian air Force was the first overseas customer for the F-15 in 1973, beating even those loyal allies Israel and Japan.
The IIAF purchased extensive numbers of both single- and two-seat versions, with the F-15As (soon upgraded to F-15Cs) being primarily operated in the air to air role, and the F-15B/D versions taking the the strike, CAS, SEAD and other air to ground roles.
The F-15C squadrons had a friendly rivalry with the F-14A Tomcat squadrons over who could make the most intercepts of Soviet MiG-25 overflights, and gained the type's first kills, shooting down 2 Iraqi MiG-21s for no loss in a brief clash over disputed Shatt-al-Arab waterway soon after coming into service.
The Iranians also took delivery of a number of the new FAST packs and those F-15Ds permanently fitted with them were termed the F-15D+
With the revolution in 1979 and the subsequent war with Iraq the plans for shelving the F-4s were dropped and as attrition of all types took it's toll, both single and dual seater F-15 versions of the renamed IRIAF fought hard in all of the roles given to them.
the F-15D+ was especially sought after for SEAD missions and long range strikes deep into Iraqi territory, and ultimately became legendary in Iranian media and culture after it's part in the precision strike on the H3 airfield complex.
As the Iranian F-15 fleet soldiered on into the 1990s and then the new century with international sanctions continuing to bite, a combination of Iranian espionage against US companies (leveraging the relationships between Iranian and US aerospace engineers going back to before the revolution), component purchases from China, a daring operation by Iranian Special Forces to recover the wreckage of a USAF F-15E downed over Iraq during OIF, and the defection of a Saudi pilot with his F-15S (and the body of his WSO, killed in his seat by the pilot as he leaned over to help strap the WSO in) enabled the Iranians to replicate, in looks if not full capability, the sensor/targetting pods of the F-15E Strike Eagle on their F-15D+ models. The upgraded aircraft were termed F-15D++ or 'double plus'..
In the late 2010s and into the 2020s the fleet was further upgraded with additional ECM and weapons capabilities and, like the rest of the IRIAF's combat aircraft, received a new grey camouflage scheme...
At the time of writing the IRIAF F-15 fleet continues to serve, and negotiations with both China and Russia for it's relacement by a package of either J-10/J-16/J-20 or Su-30/Su-35/Su-57 respectively are still ongoing...