Concept:
The Australian Open is one of the four Grand Slam tournaments in tennis. It is held annually in Melbourne, Australia.
• It is the first Grand Slam of the year.
• It is played on hard courts.
• Winning it is considered a major achievement.
Step 1: Understand the significance of the Australian Open.
It is one of:
\[
4 \text{ Grand Slam tournaments}
\]
along with Wimbledon, French Open, and US Open.
Step 2: Recall the 2026 winner.
The Australian Open men's singles title in 2026 was won by:
Carlos Alcaraz
Step 3: Check the other options.
• Roger Federer -- retired
• Novak Djokovic -- not winner in 2026
• Carlos Alcaraz -- correct
• Rafael Nadal -- not winner
Step 4: Final conclusion.
Hence, the correct answer is:
\[
\boxed{\text{Carlos Alcaraz}}
\]