[1] Growing up in Cologne-Kalk, Semir was a criminal in his youth; at the age of 13, he stole cars, but at one point, tried to save the life of a family that crashed into the Rhine, to no avail; the incident traumatized him since.
When he went to the German police, he was on odd ends with his father, who would later die of a heart attack (later revealed in "Happy Birthday" to have been caused by poisoning).
Starting from "Resurrection," Andrea had an affair with a lover called Robert, moving away from Semir with the children, having found his work being much too dangerous for their family, and he was no longer himself for a while.
Only when Alex Brandt joins the Cobra 11 team and copes with the current fall with him after initial problems does he regain his self-confidence.
Since "The Last Night" in the Fall 2014 season, Semir has been reunited romantically with Andrea, finalized a second time by their marriage in "East of Eden".
However, in three special 90 minutes episodes ("Unversöhnlich", "Machtlos", "Schutzlos"; 2022), it is revealed that the long-distance relationship failed, and Andrea and Semir are once again divorced, the pair splitting this time for good.
At first Semir enjoys his single life, but soon finds a new love interest, doctor Bianca Kessler (portrayed by Yasmina Djaballah).
Later episodes, however, reveal what he did in Istanbul: in order to infiltrate the city, he stole 50,000 euros in a deposit box to spend on heroin, having received word of the charges brought against his mother by the local police.
While pinning the drugs on crime lord Ahmet Takim, Semir accidentally kills the man and is imprisoned for manslaughter as a result.
Max Tauber, Dana's boyfriend and co-worker, initially makes good terms with Semir, but both start to hold grudges at each other after a fight between the former two.
His iconic silver BMW 3 Series is driven in almost every episode to scrap, though despite all the daring maneuvers and accidents, Semir rarely carries serious injuries.
In "Risk" it came to the reunion with Semir when Frank tried elucidate back in Germany the supposed death of a colleague near Mostar, while uncovering criminal activity of his former employer.
In 1997, Chief Inspector André Fux (portrayed by Mark Keller) came to Frank Stolte's exit to the motorway police station.
After Semir Gerkhan had overcome the grief over the loss of his colleague André Fux, he and Tom Kranich developed a real friendliness of men.
In "Resignation" Tom had to cope with a severe blow when his then pregnant girlfriend Elena Krüger, was killed by a car bomb, which was intended for him.
After two years Tom Kranich, now working as a go-kart instructor, returned at the request of his colleague Semir Gerkhan in "Comeback", after Jan had left.
Since this case arouses public interest and pictures of Chris are shown in the media, he can no longer work as a covert investigator and switches to the highway police.
In "Einsame Entscheidung", he left the police after an emotional case, where he was forced to shoot his girlfriend to save Semir, and swore he never wanted to go through something like this again.
After 2 years in prison for drug deals, Chief Inspector Alexander "Alex" Brandt, née Rickert (played by Vinzenz Kiefer), starts a new life in "Revolution".
Alex also has a relationship with a young boy named Felix Neuberger, who had a few recurring appearances after the pilot episode "The Dark Side".
In "Wind Chimes", Alex met his father, Frank Rickert, who had committed a crime 30 years ago and been in hiding since that.
This in turn led to his resignation from police, as he is last shown riding his Triumph Thruxton 900 on the autobahn away from the NRW after parting from Semir, intending to go find his mother in Brazil.
He is also very worried for his father Klaus (played by Michael Brandner), a former coal miner turned mechanic, who suffers from Alzheimer's disease.
In "Die besten letzten Tage", Klaus has been a testperson for a new Alzheimer's drug, which however, increases the probability of cardiac death.
During Semir's incarceration in Istanbul, detective Vicky Reisinger took over as the head inspector of the Autobahn Police, alongside plainclothes officer Max Tauber.
Initially, their relationship is turbulent, as Semir would find out of Vicky's past with a racist organized crime unit in Dortmund; however, after she saves her partner, thus proving her loyalty, they grow to become fast friends as well as a great team.
Though she recovers, this is only temporary; her dependence on painkillers to relieve the pain in the aftermath eventually takes its toll and she has to undergo dialysis until she finds a kidney donor.