Which religion has 24 great teachers called Tirthankaras?

A 'Tirthankara' (literally 'ford-maker') is a teacher who attains kevala jnana (perfect knowledge) and, while still living, guides others across the cycle of rebirth toward moksha, reaching final liberation only at the end of that life. Jain tradition holds that our present era has had exactly twenty-four such teachers — the first is Rishabhanatha and the twenty-fourth and last is Mahavira.

This fixed count of twenty-four Tirthankaras, and the term itself, belong specifically to Jain religious doctrine — so the religion described in the question is Jainism.

Distinguishing the options by what each tradition actually holds:

• Hinduism reveres Vedic rishis, sages, and divine avatars, but has no group termed 'Tirthankaras'.

• Sikhism's spiritual lineage is the ten Sikh Gurus, from Guru Nanak to Guru Gobind Singh — a count of ten Gurus, not twenty-four Tirthankaras.

• Buddhism speaks of the historical Buddha and other Buddhas across ages, but does not use the title 'Tirthankara' or fix their number at twenty-four.

Since only Jain doctrine defines both the exact term 'Tirthankara' and the count of twenty-four, Jainism is confirmed as the answer independent of the other options.