Now that Alexei Navalny has been barred from the elections Vladimir Putin will be the only candidate in the Russian elections to be held next year. Is it illegal to bar a candidate even though he is eligible? This might set a precedent where powerful rulers might bar other candidates from taking part in the elections.
Navalny has been barred from standing in the election due to a conviction on corruption charges, and because of his outstanding criminal record by Russian law this means he cannot run for president.
After his first trial for these corruption charges the European Court of Human Rights ruled that his trial was unfair and demanded a retrial, following which the ruling was overturned, sent back to a lower court, and that lower court affirmed the corruption charges.
In this sense from an internal legal standpoint the elections are legitimate, but the real question at hand is whether the trials themselves were fair or whether Putin and/or his administration are manipulating the courts to keep what most view as the only legitimate challenge to Putin's rule out of the election. As with the assassination of Boris Nemtsov, it reeks of foul play but it is challenging to prove anything.