Whether they made lessons fun, ignited your passion for learning or helped you through a difficult time, that person was a big part of your childhood you will never forget.
This retro photo gallery shows much-loved teachers at schools around Northern Ireland with their pupils during the noughties.
Perhaps your favourite teacher is among them, or maybe you will spot an old school friend.
What are your happiest memories of your school days? Let us know in the comments section.
21. Drumadonnell Primary School
P1 teacher Mrs Bingham pictured at Drumadonnell Primary School in 2006 with pupils, Jonathan, Robert, Ethan, Sam, Ethan, Steven and Scott | National World Photo: Michael Cousins
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22. St Mary's Primary School
P1 teacher Sharon Cooney pictured in 2008 at St Mary's Primary School, Derrymore, with pupils Jay Wylie and Eion Brown | National World Photo: Geoffrey Cousins
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23. Maralin Village Primary School
P1 teacher Suzanne Guy pictured in 2008 at Maralin Village Primary School with pupils Thomas Urwin, Adam Thompson, Jesse Millar and Beth Heasley on the stepping stones | National World Photo: Geoffrey Cousins
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24. St Francis Primary School
Ban Kathryn De Brun, rang 1 teacher at St Francis Primary School, with pupils James McEnery and Aodhan Haughian in 2008 | National World Photo: Geoffrey Cousins