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.
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5. St Anthony's Primary School
P1 teacher Mrs Christine McGeown with pupils Clodagh Thompson and Aoife Clarke at St Anthony's Primary School in 2007 | National World Photo: Geoffrey Cousins
6. St Patrick's Primary School
P1 teacher Dana Magee with new pupil Katie Byrne at St Patrick's Primary School, Aghagallon, in 2007 | National World Photo: Geoffrey Cousins
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7. Glynn Primary School
P3 pupil Robbie Ferguson with teacher Miss Johnston at Glynn Primary School in 2009 | Other Photo: Other
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8. St Mary's Primary School
Catherine McMahon, aged 7, from St Mary's Primary School, Derrytrasna, winner of the First Trust Bank, Lurgan, Christmas Colouring Competition for 7 years and under, receives her prize from Michelle Forde, bank student officer, in . They are pictured with school principal Joan Aldridge and teacher Sarah Coleman. | National World Photo: Geoffrey Cousins